Add github workflow for tox-based testing

Use LRU cache for shape transformation

Only cache transform if shapes are actually the same

readme: Update description

Merge pull request #28 from mysablehats/master

Fixes inconsistent fps issues (fps reading vs fps writing)

Fix input parsing regression

- Invalid input paths were accidentally ignored instead of triggering
  error messages
- The "$ deface cam" shortcut wasn't working properly

Update documentation and apply PEP8

readme: Add docs on high-res media issues, --scale

Update repository location