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
Merge branch 'transforms-subpackage' into transform-cache

Conflicts:
	vispy/scene/transforms.py
Implemented basic transform caching; testing needed.
Corrections to SceneEvent transforms
Fixed transform issues; more testing needed
Fixed transform cache handling
Optimization
Fixed bugs
Merge branch 'master' into transform-cache

Conflicts:
	vispy/scene/transforms/__init__.py
Added grid_large example and grid startup optimizations
Added transform caching to mouse events
Optimizations for grid_large
Add Texture.__repr__
minor edits
Made app.run() do nothing
Added note about SceneCanvas use of TransformCache