Fix for Issue #840 - URL pattern too broad

[rappdw]

Changed _URL_PATTERN in language/tokenizer_exceptions.py, using url regex validation pattern from: https://mathiasbynens.be/demo/url-regex

Description

This change will screen out a number of patterns that are not URLs as well as picking up some patterns that were missed.
Test cases were added to test_urls to expose the issue and validate the fix.

Types of changes

• [ x] Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality to spaCy)
• Breaking change (fix or feature causing change to spaCy's existing functionality)
• Documentation (addition to documentation of spaCy)

Checklist:

• My change requires a change to spaCy's documentation.
• I have updated the documentation accordingly.
• [x ] I have added tests to cover my changes.
• All new and existing tests passed.

[honnibal]

🎉
Awesome before and after here --- thanks for taking the time to lay out the regex nicely (not always easy!).