As per https://guides.rubygems.org/specification-reference/#metadata,
add metadata to the gemspec file. This'll allow people to more easily
access the source code, raise issues and read the changelog. These
`bug_tracker_uri`, `changelog_uri`, `documentation_uri`,
`source_code_uri`, and `wiki_uri` links will appear on the rubygems page
at https://rubygems.org/gems/thor and be available via the rubygems API
after the next release.

When creating a symlink, the source path may be relative to the destination. If
this is the case, #identical? fails becase it interprets it as an absolute path.
Update #identical to resolve the source path before comparing.

Make deprecation_warning available in Thor::Base and Thor::Option when
"thor" is not required, by moving it to "lib/thor/base.rb" which will
be required.

[Fixes #703]

Move deprecation_warning to lib/thor/base.rb

Add project metadata to the gemspec

Handle relative source path in create_link #identical?