Add method to reconstruct the request URI from a WSGI environment.

[amcgregor]

Add method to reconstruct the request URI from a WSGI environment.

[amcgregor]

Initial commit, above, adds the factory method URI.from_wsgi which may be passed a WSGI environment dictionary or dictionary-alike, or any object which has an environ attribute that is a WSGI environment dictionary, such as a WebOb Request instance. Tests forthcoming (having a mild issue with it emitting the default port number for the given protocol) but in-progress.

pytest current test failure

    def test_wsgi_unpacking():
        webob = pytest.importorskip('webob')
    
        url = 'https://example.com/foo/bar?baz=27'
    
        request = webob.Request.blank(url)
        uri = URI.from_wsgi(request)
    
>       assert str(uri) == url
E    AssertionError: assert 'https://exam...oo/bar?baz=27' == 'https://exam...oo/bar?baz=27'
E      - https://example.com/foo/bar?baz=27
E      + https://example.com:443/foo/bar?baz=27
E      ?                    ++++

request    = <Request at 0x108fd1100 GET https://example.com/foo/bar?baz=27>
uri        = URI('https://example.com:443/foo/bar?baz=27')
url        = 'https://example.com/foo/bar?baz=27'
webob      = <module 'webob' from '/Users/amcgregor/Projects/marrow/.venv/lib/python3.8/site-packages/webob/__init__.py'>

[amcgregor]

Sub-optimally corrected by inclusion of the two likely culprits in a WSGI environment (http and https) in a port mapping dictionary uri.uri:SERVICES; this should be loaded from /etc/services or such a file should be bundled with the library, ref: #15. (System-provided eliminates maintenance overhead for this file.)