Add a new Check to ensure package filename matches the package info name.

Closes #136 (closed)

Add a new Check to ensure package filename matches the package info name.

docs/repod/changelog.rst: Document the new package name check.

repod/action/check.py: Add a new MatchingFilenameCheck which checks that the package filename matches the package's metadata.

repod/action/task.py: Add a MatchingFilenameCheck when creating a new package.

tests/action/test_check.py: Add tests to ensure the MatchingFilenameCheck works correctly.