removed getExtension() + improved parsing of "Season Episode" filenames

The getExtension function became a bit superfluous as it is only called
once and could be reduced to a one-liner.

Fixed bug for "Season Episode" syntax in filenames which was misnaming
files with double digit episodes or mp4 extension. Wrote a test and
made the corresponding regex non-greedy.
Stats file to prevent overwrite

Will check destination file before attempting to write.
--force flag added to force overwriting of files
Added todo.otl file to .gitignore.
README updated to include force flag and new offset syntax
Errors handled a bit better :-S
Improved arg handling

Alias for existing flags
- -S, --show
- -s, --season
- -o, --offset
- -f, --force

New help option (-h, --help)
Gets shouty if no args passed.
Gets shouty if args passed aren't existing files
Removed optionalParams function (it was too weird and hacky :/)
--episode flag works, plus test