Merge pull request #12 from minexew/master

Fix some things that had been wrong from the beginning
Merge pull request #14 from minexew/master

Fix incorrect simplification of Matrix4f multiplication
Merge pull request #18 from minexew/master

Implement stream-based PNG reading; add class ArrayStream
Added new imports in package modules
Added cast from StreamPos to size_t in pos
Fixed #16
Removed deprecated transform method
Merge pull request #21 from minexew/master

Make Stream-related functions final methods of the respective interfaces
Merge branch 'master' of https://github.com/gecko0307/dlib into filesystem