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/mg_coap_parse.md

@@ -0,0 +1,22 @@
+---
+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()` 
+