fix: an edge case bug that could potentially cause data loss when generating the final folder
fix: a bug where the encode would attempt to use the source index file, generating a new one in it's place incorrectly (this was present in ffms2)
feat: add arg `--img-lib`. This allows the user to select one of the two image libs, defaulting to fpng.
refactor: improved error handling
feat: added temp directory clean up even if the program crashes
refactor: removed --index-dir arg
feat: added --source-index-path and --encode-index-path, these are direct paths to the index file vs only having a directory to search
refactor: added a more descriptive help message for --subtitle-color
