Adds a post commit hook to notify devs of tests relating changed files

Now that we have common/automation/webdriver/static_files/knows_out.yml,
it doesn't hurt to simply notify devs of the impact their code changes.

squashed commit of:
- Updates the Ruby parser to do most of the heavy lifting
- Catches any runtime Yaml parsing issues
- Only calls this Ruby script once
- No new dependencies required.
- Ruby is awesome
- Cleans up bash script to me more readable + extras
- No longer depends on pcregrep
- Uses Ruby's YAML parser, which is in std lib since 1.9.3