Add paths param to ./check

* This will check for changes in files that match the "paths" param
* The "paths" param is passed straight to git log, grabbing the last
  commit that that any of the files matched were touched

Maybe this could be even further improved by adding the option to ignore paths? We could do that we something like:

```bash
if [ -n "$ignore_paths" ]; then
  grep_files=''
  for ignore_path in $ignore_paths; do
    grep_files="${grep_files}\|${ignore_path}"
  done
  paths=$(git ls-files | grep -v $grep_files)
fi

# ... go on to current implementation
```

That way you can ignore files, which potentially is a shorter list.