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/dns-server.h/intro.md

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+---
+title: "DNS server"
+symbol_kind: "intro"
+decl_name: "dns-server.h"
+---
+
+Disabled by default; enable with `-DMG_ENABLE_DNS_SERVER`.
+

docs/c-api/dns-server.h/items.json

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+{
+    "items": [
+        {
+            "type": "markdown",
+            "name": "intro.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_dns_create_reply.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_dns_reply_record.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mg_dns_send_reply.md"
+        }
+    ]
+}

docs/c-api/dns-server.h/mg_dns_create_reply.md

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+---
+title: "mg_dns_create_reply()"
+decl_name: "mg_dns_create_reply"
+symbol_kind: "func"
+signature: |
+  struct mg_dns_reply mg_dns_create_reply(struct mbuf *io,
+                                          struct mg_dns_message *msg);
+---
+
+Create a DNS reply.
+
+The reply will be based on an existing query message `msg`.
+The query body will be appended to the output buffer.
+"reply + recursion allowed" will be added to the message flags and
+message's num_answers will be set to 0.
+
+Answer records can be appended with `mg_dns_send_reply` or by lower
+level function defined in the DNS API.
+
+In order to send the reply use `mg_dns_send_reply`.
+It's possible to use a connection's send buffer as reply buffers,
+and it will work for both UDP and TCP connections.
+
+Example:
+
+```c
+reply = mg_dns_create_reply(&nc->send_mbuf, msg);
+for (i = 0; i < msg->num_questions; i++) {
+  rr = &msg->questions[i];
+  if (rr->rtype == MG_DNS_A_RECORD) {
+    mg_dns_reply_record(&reply, rr, 3600, &dummy_ip_addr, 4);
+  }
+}
+mg_dns_send_reply(nc, &reply);
+``` 
+

docs/c-api/dns-server.h/mg_dns_reply_record.md

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+---
+title: "mg_dns_reply_record()"
+decl_name: "mg_dns_reply_record"
+symbol_kind: "func"
+signature: |
+  int mg_dns_reply_record(struct mg_dns_reply *reply,
+                          struct mg_dns_resource_record *question,
+                          const char *name, int rtype, int ttl, const void *rdata,
+                          size_t rdata_len);
+---
+
+Append a DNS reply record to the IO buffer and to the DNS message.
+
+The message num_answers field will be incremented. It's caller's duty
+to ensure num_answers is propertly initialized.
+
+Returns -1 on error. 
+

docs/c-api/dns-server.h/mg_dns_send_reply.md

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+---
+title: "mg_dns_send_reply()"
+decl_name: "mg_dns_send_reply"
+symbol_kind: "func"
+signature: |
+  void mg_dns_send_reply(struct mg_connection *nc, struct mg_dns_reply *r);
+---
+
+Send a DNS reply through a connection.
+
+The DNS data is stored in an IO buffer pointed by reply structure in `r`.
+This function mutates the content of that buffer in order to ensure that
+the DNS header reflects size and flags of the mssage, that might have been
+updated either with `mg_dns_reply_record` or by direct manipulation of
+`r->message`.
+
+Once sent, the IO buffer will be trimmed unless the reply IO buffer
+is the connection's send buffer and the connection is not in UDP mode. 
+