clean up some block capture issues
specifically skip disk cache for managed caching requests
fixes for improperly nil'ing and relying on nil'd weak pointers
setter should default to unanimated
Revert "remove v4 API support"

This reverts commit acd5ed37d1d0b5f2e33f3c318856c1c21f808562.
fixes #494: bring back v4 tiles including 512px for retina
update docs re: v4 sizes
Merge with upstream