Add .NET config files as XML
Fix package.config to packages.config
 add pants BUILD file highlighting to languages.yml

the pants build tool uses python files named BUILD. This adds highlighting for them.
Add Language.find_by_extension
Add some tests for Language.find_by_extension
Fix docs
Allow extensions without a leading dot

This makes the API a little easier to use.
Merge pull request #1683 from github/find-by-ext

Extract Language.find_by_extension
Bumping to 3.5.0
Merge pull request #1694 from github/cut-release-v3.5.0

Bumping to 3.5.0
Make it safe to pass nil to Language.find_by_name/alias again

This restores compatibility with v3.4.x.
Merge pull request #1695 from github/nil-safety

Make it safe to pass nil to Language.find_by_name/alias again
Bump to 3.5.1
Merge pull request #1696 from github/cut-release-v3.5.1

Bump to 3.5.1
Merge pull request #1657 from techniq/patch-1

Add .NET config files as XML
Merge pull request #1653 from baroquebobcat/patch-1

add pants BUILD file highlighting to languages.yml