Bug fix and improved --help documentation

- Fixed a bug where a non-existent file would be "converted" resulting in an empty .vtt file. Users are now notified if the input path does not exist.
- Better wording in --help documentation. Also added a missing parenthesis.
- Bumped version to 1.0.1
- Updated Windows binary
Merge branch 'master' of https://github.com/woollybogger/srt-to-vtt-cl