Merge pull request #27 from OddBloke/master

Use `file` to determine which files are Python files
Add test for files_for_commit.
Add pdb tests.
Optionally filter out files in pdb.
Merge pull request #30 from alexcouper/master-add-pdb-test

Master add pdb test
Add --version command.
Merge pull request #31 from alexcouper/master-version-output

Add --version command.
Rewrite the header of the pre-commit hook to use virtualenv python.
Only point at virtualenv Python if -e given.
Merge pull request #26 from OddBloke/work_outside_virtualenv

[RFC] Use Python executable at install time to run pre-commit hook
Minor fixes to use-virtualenv-python.
Merge pull request #33 from alexcouper/work_outside_virtualenv

Minor fixes to use-virtualenv-python.
Update changelog.