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_handshake2.md

@@ -0,0 +1,19 @@
+---
+title: "mg_send_websocket_handshake2()"
+decl_name: "mg_send_websocket_handshake2"
+symbol_kind: "func"
+signature: |
+  void mg_send_websocket_handshake2(struct mg_connection *nc, const char *path,
+                                    const char *host, const char *protocol,
+                                    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, `host` goes into the `Host` header, `protocol` goes into the
+`Sec-WebSocket-Proto` header (NULL to omit), extra_headers` is extra HTTP
+headers to send or `NULL`.
+
+This function is intended to be used by websocket client. 
+