Added new example showing offscreen rendering (GPGPU example here) without any visible window.
ipynb_static backend
This backend allows us to draw a single png image onto IPython notebook.
- It imports `display_png` from `IPython.display`
- Takes a screenshot, converts it to PNG and encodes with base64
- Displays it with `display_png` on `canvas.show()`
Add examples
Added profiling command line flag
ModularProgram now correctly triggers ModularVisual.update
give SceneCanvas symbolic Entities to represent ndc, fb, and lpx coordinate systems
Break scene.transforms into subpackage
Merge branch 'transforms-subpackage' into transform-cache

Conflicts:
	vispy/scene/transforms.py
Rename Transform => BaseTransform
Fix unit test
Added note about basetransform - chaintransform cyclic import
Make transform imports explicit
flakify
Add scene.transforms to setup.py
Modified ModularVisual to check dimension of color, added reactive polygon test and added color to visuals and examples

Minor fix post rebase

Fixed spelling mistake

Added reactive ellipse tests
Implement (partly) proper way to inherit from Entity

That is, each Subclass does `__init__(what=None, I=3, need=3, **kwargs)`
and then `SuperClass.__init__(self, **kwargs)`

Also fixes to Text class and SceneCanvas can be other bgcolor than
black :)
Changed coordinates of test visuals
Added reactive regular polygon tests
Fixed  regular polygon tests
Implemented basic transform caching; testing needed.