Add import to example

Closes #224
I, for one, welcome our new @matthewwithanm overlords.
Update installation directions; closes #223
Remove unused imports
PEP 3110 compat
Test stringification of LazyImageCacheFiles
Fix LazyImageCacheFile.__repr__ and __str__

Using SimpleLazyObject also lets us clean things up a bit.

Closes #218
Fix cache backend fallback

Closes #225
Closes #226
Bump version to 3.0.1.
Merge branch 'release/3.0.1'

* release/3.0.1:
  Bump version to 3.0.1.
  Fix cache backend fallback
  Fix LazyImageCacheFile.__repr__ and __str__
  Test stringification of LazyImageCacheFiles
  PEP 3110 compat
  Remove unused imports
  Update installation directions; closes #223
  I, for one, welcome our new @matthewwithanm overlords.
  Add import to example