Metadata-parser

* created `MetadataParser.get_url_canonical`
* created `MetadataParser.get_url_opengraph`
* `MetadataParser.get_discrete_url` now calls `get_url_canonical` and `get_url_opengraph`

* fixed packaging error. removed debug "print" statements

* upgrade nested local canonical rels correctly

* added a new `_internal` storage namespace to the `MetadataParser.metadata` payload.
this simply stashes the `MetadataParser.url` and `MetadataParser.url_actual` attributes to makes objects easier to encode for debugging
* the twitter parsing was incorrectly looking for 'value' not 'content' as in the current spec
* tracking the shortlink on a page

- This has a default behavior change regarding `get_discrete_url()` .
- `is_parsed_valid_url()` did not correctly handle `require_public_netloc=True`, and would allow for `localhost` values to pass
- new kwarg `allow_localhosts` added to
* is_parsed_valid_url
* is_url_valid
* url_to_absolute_url
* MetadataParser.__init__
* MetadataParser.absolute_url
* MetadataParser.get_discrete_url
* MetadataParser.get_metadata_link
- new method `get_fallback_url`
- `url_to_absolute_url` will return `None` if not supplied with a fallback and test url. Previously an error in parsing would occur
- `url_to_absolute_url` tries to do a better job at determining the intended url when given a malformed url.

- packaging fixes