Make mg_connect_{http,ws} use mg_parse_uri

Remove the specialized URI parser, clean up code a bit.

Fix parsing of URIs with IPv6 hosts (http://[2001:2:3::4]:567/)

PUBLISHED_FROM=968ad97585d928123106ce3828920ee073113f83

docs/c-api/http.h/mg_send_websocket_handshake3v.md

@@ -0,0 +1,17 @@
+---
+title: "mg_send_websocket_handshake3v()"
+decl_name: "mg_send_websocket_handshake3v"
+symbol_kind: "func"
+signature: |
+  void mg_send_websocket_handshake3v(struct mg_connection *nc,
+                                     const struct mg_str path,
+                                     const struct mg_str host,
+                                     const struct mg_str protocol,
+                                     const struct mg_str extra_headers,
+                                     const struct mg_str user,
+                                     const struct mg_str pass);
+---
+
+Same as mg_send_websocket_handshake3 but with strings not necessarily
+NUL-temrinated 
+