Enabled support for custom contexts

Layer.js - added ContextManager class
Layer.js - added Context2d class that is just giving access to standard 2d context from canvas
Layer now personally holds the shift

Layer.js - finalized support for camera shifting

NOTE: add all functions and function overlays to context overlay
Merge pull request #8 from CoreTec/0.00.0004-E

0.00.0004 e