Metadata-parser

- formatting fixes via flake8

- Lightweight, but functional, url validation
-- new 'init' argument (defaults to True) : `require_public_netloc`
-- this will ensure a url's hostname/netloc is either an IPV4 or "public DNS" name
-- if the url is entirely numeric, requires it to be IPV4
-- if the url is alphanumeric, requires a TLD + Domain ( exception is "localhost" )
-- this is NOT RFC compliant, but designed for "Real Life" use cases.

- Several fixes to improve support of canonical and absolute urls
-- replaced REGEX parsing of urls with `urlparse` parsing and inspection; too many edge cases got in
-- refactored `MediaParser.absolute_url` , now proxies a call to new function `url_to_absolute_url`
-- refactored `MediaParser.get_discrete_url` , now cleaner and leaner.
-- refactored how some tests run, so there is cleaner output

- trying to fix some issues with distribution

- trying to parse unparsable pages was creating an error
-- `MetadataParser.init` now accepts `only_parse_file_extensions` -- list of the only file extensions to parse
-- `MetadataParser.init` now accepts `force_parse_invalid_content_type` -- forces to parse invalid content
-- `MetadataParser.fetch_url` will only parse "text/html" content by default

- trying to ensure we return a valid url in get_discrete_url()
- adding in some proper unit tests; migrating from the private demo's slowly ( the private demo's hit a lot of internal files and public urls ; wouldn't be proper to make these public )
- setting `self.url_actual = url` on __init__. this will get overridden on a `fetch`, but allows for a fallback on html docs passed through