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/http.h/mg_send_websocket_handshake.md

@@ -0,0 +1,22 @@
+---
+title: "mg_send_websocket_handshake()"
+decl_name: "mg_send_websocket_handshake"
+symbol_kind: "func"
+signature: |
+  void mg_send_websocket_handshake(struct mg_connection *nc, const char *uri,
+                                   const char *extra_headers);
+---
+
+Send websocket handshake to the server.
+
+`nc` must be a valid connection, connected to a server. `uri` is an URI
+to fetch, extra_headers` is extra HTTP headers to send or `NULL`.
+
+This function is intended to be used by websocket client.
+
+Note that the Host header is mandatory in HTTP/1.1 and must be
+included in `extra_headers`. `mg_send_websocket_handshake2` offers
+a better API for that.
+
+Deprecated in favour of `mg_send_websocket_handshake2` 
+