Remove old docs, rename docs_new to docs

It would be probably good idea to also remove tools/docgen.py and
asciidoc.mk, but asciidoc.mk is still mentioned under `cloud/doc`, which
may contain some useful info which we'll need at least to review before
removing.

PUBLISHED_FROM=faf454d4c52a2f07ea8ac084cf0bd11a0c9c9b3b

docs/c-api/coap.h/intro.md

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+---
+title: "CoAP"
+symbol_kind: "intro"
+decl_name: "coap.h"
+---
+
+CoAP message format:
+
+```
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
+|Ver| T | TKL | Code | Message ID | Token (if any, TKL bytes) ...
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
+| Options (if any) ...            |1 1 1 1 1 1 1 1| Payload (if any) ...
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
+```
+

docs/c-api/coap.h/items.json

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+{
+    "items": [
+        {
+            "type": "markdown",
+            "name": "intro.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_set_protocol_coap.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_coap_add_option.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_coap_free_options.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_coap_send_message.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_coap_send_ack.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_coap_parse.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_coap_compose.md"
+        },
+        {
+            "type": "markdown",
+            "name": "struct_mg_coap_option.md"
+        },
+        {
+            "type": "markdown",
+            "name": "struct_mg_coap_message.md"
+        }
+    ]
+}

docs/c-api/coap.h/mg_coap_add_option.md

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+---
+title: "mg_coap_add_option()"
+decl_name: "mg_coap_add_option"
+symbol_kind: "func"
+signature: |
+  struct mg_coap_option *mg_coap_add_option(struct mg_coap_message *cm,
+                                            uint32_t number, char *value,
+                                            size_t len);
+---
+
+Add new option to mg_coap_message structure.
+Returns pointer to the newly created option. 
+

docs/c-api/coap.h/mg_coap_compose.md

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+---
+title: "mg_coap_compose()"
+decl_name: "mg_coap_compose"
+symbol_kind: "func"
+signature: |
+  uint32_t mg_coap_compose(struct mg_coap_message *cm, struct mbuf *io);
+---
+
+Composes CoAP message from mg_coap_message structure.
+This is a helper function.
+Return value: see `mg_coap_send_message()` 
+

docs/c-api/coap.h/mg_coap_free_options.md

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+---
+title: "mg_coap_free_options()"
+decl_name: "mg_coap_free_options"
+symbol_kind: "func"
+signature: |
+  void mg_coap_free_options(struct mg_coap_message *cm);
+---
+
+Free the memory allocated for options,
+if cm paramater doesn't contain any option does nothing. 
+

docs/c-api/coap.h/mg_coap_parse.md

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+---
+title: "mg_coap_parse()"
+decl_name: "mg_coap_parse"
+symbol_kind: "func"
+signature: |
+  uint32_t mg_coap_parse(struct mbuf *io, struct mg_coap_message *cm);
+---
+
+Parse COAP message and fills mg_coap_message and returns cm->flags.
+This is a helper function.
+
+NOTE: usually CoAP work over UDP, so lack of data means format error,
+but in theory it is possible to use CoAP over TCP (according to RFC)
+
+The caller have to check results and treat COAP_NOT_ENOUGH_DATA according to
+underlying protocol:
+
+- in case of UDP COAP_NOT_ENOUGH_DATA means COAP_FORMAT_ERROR,
+- in case of TCP client can try to receive more data
+
+Return value: see `mg_coap_send_message()` 
+

docs/c-api/coap.h/mg_coap_send_ack.md

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+---
+title: "mg_coap_send_ack()"
+decl_name: "mg_coap_send_ack"
+symbol_kind: "func"
+signature: |
+  uint32_t mg_coap_send_ack(struct mg_connection *nc, uint16_t msg_id);
+---
+
+Compose CoAP acknowledgement from `mg_coap_message`
+and send it into `nc` connection.
+Return value: see `mg_coap_send_message()` 
+

docs/c-api/coap.h/mg_coap_send_message.md

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+---
+title: "mg_coap_send_message()"
+decl_name: "mg_coap_send_message"
+symbol_kind: "func"
+signature: |
+  uint32_t mg_coap_send_message(struct mg_connection *nc,
+                                struct mg_coap_message *cm);
+---
+
+Compose CoAP message from `mg_coap_message`
+and send it into `nc` connection.
+Return 0 on success. On error, it is a bitmask:
+
+- `#define MG_COAP_ERROR 0x10000`
+- `#define MG_COAP_FORMAT_ERROR (MG_COAP_ERROR | 0x20000)`
+- `#define MG_COAP_IGNORE (MG_COAP_ERROR | 0x40000)`
+- `#define MG_COAP_NOT_ENOUGH_DATA (MG_COAP_ERROR | 0x80000)`
+- `#define MG_COAP_NETWORK_ERROR (MG_COAP_ERROR | 0x100000)` 
+

docs/c-api/coap.h/mg_set_protocol_coap.md

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+---
+title: "mg_set_protocol_coap()"
+decl_name: "mg_set_protocol_coap"
+symbol_kind: "func"
+signature: |
+  int mg_set_protocol_coap(struct mg_connection *nc);
+---
+
+Set CoAP protocol handler - trigger CoAP specific events 
+

docs/c-api/coap.h/struct_mg_coap_message.md

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+---
+title: "struct mg_coap_message"
+decl_name: "struct mg_coap_message"
+symbol_kind: "struct"
+signature: |
+  struct mg_coap_message {
+    uint32_t flags;
+    uint8_t msg_type;
+    uint8_t code_class;
+    uint8_t code_detail;
+    uint16_t msg_id;
+    struct mg_str token;
+    struct mg_coap_option *options;
+    struct mg_str payload;
+    struct mg_coap_option *optiomg_tail;
+  };
+---
+
+CoAP message. See RFC 7252 for details. 
+

docs/c-api/coap.h/struct_mg_coap_option.md

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+---
+title: "struct mg_coap_option"
+decl_name: "struct mg_coap_option"
+symbol_kind: "struct"
+signature: |
+  struct mg_coap_option {
+    struct mg_coap_option *next;
+    uint32_t number;
+    struct mg_str value;
+  };
+---
+
+CoAP options.
+Use mg_coap_add_option and mg_coap_free_options
+for creation and destruction. 
+