MINOR: http: implement http uri parser

MINOR: http: implement http uri parser

Implement a http uri parser type. This type will be used as a context to
parse the various elements of an uri.

The goal of this serie of patches is to factorize duplicated code
between the http_get_scheme/authority/path functions. A simple parsing
API is designed to be able to extract once each element of an HTTP URI
in order. The functions will be renamed in the following patches to
reflect the API change with the prefix http_parse_*.

For the parser API, the http_uri_parser type must first be
initialized before usage. It will register the URI to parse and detect
its format according to the rfc 7230.