Optimize Documentation Images to Save Bandwidth

This commit optimizes the images available in the
docs folder in order to  save  on  bandwidth  and
also decrease page loading time.

Images updated:
- docs/Array.png
- docs/ArrayBridge.png
- docs/ArrayCast.png
- docs/ArrayImplementation.png
- docs/ContiguousArray.png
- docs/Slice.png

Author: daknob