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/net.h/mg_send.md

@@ -0,0 +1,14 @@
+---
+title: "mg_send()"
+decl_name: "mg_send"
+symbol_kind: "func"
+signature: |
+  void mg_send(struct mg_connection *, const void *buf, int len);
+---
+
+Send data to the connection.
+
+Note that sending functions do not actually push data to the socket.
+They just append data to the output buffer. MG_EV_SEND will be delivered when
+the data has actually been pushed out. 
+