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_connect_http_opt.md

@@ -0,0 +1,18 @@
+---
+title: "mg_connect_http_opt()"
+decl_name: "mg_connect_http_opt"
+symbol_kind: "func"
+signature: |
+  struct mg_connection *mg_connect_http_opt(struct mg_mgr *mgr,
+                                            mg_event_handler_t ev_handler,
+                                            struct mg_connect_opts opts,
+                                            const char *url,
+                                            const char *extra_headers,
+                                            const char *post_data);
+---
+
+Helper function that creates outbound HTTP connection.
+
+Mostly identical to mg_connect_http, but allows to provide extra parameters
+(for example, SSL parameters 
+