instantiate Bounds from string
Allow single-dimension bounds from strings
When resizing if either dimension is 0, maintain aspect ratio
add subrectangle copying (image cropping)
expose NewCropped
add basic tests for NewCropped
Fix compilation of example.
Run go-fmt on the repo.
Error handling instead of nil-checks. Stub errors need to be improved.
Add docs. Fix tests.
Don't create files during tests.
Add package doc.
Merge pull request #1 from aybabtme/api_work

Add docs, more errors, fix tests, add examples.