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_url_decode.md

@@ -13,6 +13,7 @@ Source string is specified by (`src`, `src_len`), and destination is
 (`dst`, `dst_len`). If `is_form_url_encoded` is non-zero, then
 `+` character is decoded as a blank space character. This function
 guarantees to NUL-terminate the destination. If destination is too small,
-then the source string is partially decoded and `-1` is returned. Otherwise,
+then the source string is partially decoded and `-1` is returned.
+*Otherwise,
 a length of the decoded string is returned, not counting final NUL.