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/mbuf.h/intro.md

@@ -0,0 +1,11 @@
+---
+title: "Memory Buffers"
+symbol_kind: "intro"
+decl_name: "mbuf.h"
+---
+
+Mbufs are mutable/growing memory buffers, like C++ strings.
+Mbuf can append data to the end of a buffer, or insert data into arbitrary
+position in the middle of a buffer. The buffer grows automatically when
+needed.
+

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

@@ -0,0 +1,40 @@
+{
+    "items": [
+        {
+            "type": "markdown",
+            "name": "intro.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_init.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_free.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_append.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_insert.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_remove.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_resize.md"
+        },
+        {
+            "type": "markdown",
+            "name": "mbuf_trim.md"
+        },
+        {
+            "type": "markdown",
+            "name": "struct_mbuf.md"
+        }
+    ]
+}

docs/c-api/mbuf.h/mbuf_append.md

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+---
+title: "mbuf_append()"
+decl_name: "mbuf_append"
+symbol_kind: "func"
+signature: |
+  size_t mbuf_append(struct mbuf *, const void *data, size_t data_size);
+---
+
+Appends data to the Mbuf.
+
+Return the number of bytes appended, or 0 if out of memory. 
+

docs/c-api/mbuf.h/mbuf_free.md

@@ -0,0 +1,10 @@
+---
+title: "mbuf_free()"
+decl_name: "mbuf_free"
+symbol_kind: "func"
+signature: |
+  void mbuf_free(struct mbuf *);
+---
+
+Free the space allocated for the mbuffer and resets the mbuf structure. 
+

docs/c-api/mbuf.h/mbuf_init.md

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+---
+title: "mbuf_init()"
+decl_name: "mbuf_init"
+symbol_kind: "func"
+signature: |
+  void mbuf_init(struct mbuf *, size_t initial_capacity);
+---
+
+Initialize an Mbuf.
+`initial_capacity` specifies the initial capacity of the mbuf. 
+

docs/c-api/mbuf.h/mbuf_insert.md

@@ -0,0 +1,14 @@
+---
+title: "mbuf_insert()"
+decl_name: "mbuf_insert"
+symbol_kind: "func"
+signature: |
+  size_t mbuf_insert(struct mbuf *, size_t, const void *, size_t);
+---
+
+Insert data at a specified offset in the Mbuf.
+
+Existing data will be shifted forwards and the buffer will
+be grown if necessary.
+Return the number of bytes inserted. 
+

docs/c-api/mbuf.h/mbuf_remove.md

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+---
+title: "mbuf_remove()"
+decl_name: "mbuf_remove"
+symbol_kind: "func"
+signature: |
+  void mbuf_remove(struct mbuf *, size_t data_size);
+---
+
+Remove `data_size` bytes from the beginning of the buffer. 
+

docs/c-api/mbuf.h/mbuf_resize.md

@@ -0,0 +1,13 @@
+---
+title: "mbuf_resize()"
+decl_name: "mbuf_resize"
+symbol_kind: "func"
+signature: |
+  void mbuf_resize(struct mbuf *, size_t new_size);
+---
+
+Resize an Mbuf.
+
+If `new_size` is smaller than buffer's `len`, the
+resize is not performed. 
+

docs/c-api/mbuf.h/mbuf_trim.md

@@ -0,0 +1,10 @@
+---
+title: "mbuf_trim()"
+decl_name: "mbuf_trim"
+symbol_kind: "func"
+signature: |
+  void mbuf_trim(struct mbuf *);
+---
+
+Shrink an Mbuf by resizing its `size` to `len`. 
+

docs/c-api/mbuf.h/struct_mbuf.md

@@ -0,0 +1,14 @@
+---
+title: "struct mbuf"
+decl_name: "struct mbuf"
+symbol_kind: "struct"
+signature: |
+  struct mbuf {
+    char *buf;   /* Buffer pointer */
+    size_t len;  /* Data length. Data is located between offset 0 and len. */
+    size_t size; /* Buffer size allocated by realloc(1). Must be >= len */
+  };
+---
+
+Memory buffer descriptor 
+