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/mbuf_init.md

@@ -0,0 +1,11 @@
+---
+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. 
+