added graphitem

- ViewBox ignore bounds on zoom box
- Fixed improper pixel size caching
- Fixed check for 'win' in sys.platform (matches 'darwin' as well)

added method for setting axis tick font

Fixed linearRegionItem hilight when not movable

Bugfix in GraphicsItem.pixelVectors
Fixes for PySide and Python3

  - GraphicsItem.pixelVectors copies cached results before returning
  - Multiprocess fixes for Windows:
      - mmap/shm uses anonymous maps rather than tempfiles
      - avoid use of getppid and setpgrp
      - work around hmac authentication bug (use os.urandom to generate key)

  - AxisItem shows fewer tick levels in some cases.
  - Lots of boundingRect and dataBounds caching
    (improves ViewBox auto-range performance, especially with multiple plots)
  - GraphicsScene avoids testing for hover intersections with non-hoverable items
    (much less slowdown when moving mouse over plots)

Improved performance for remote plotting:
  - reduced cost of transferring arrays between processes (pickle is too slow)
  - avoid unnecessary synchronous calls

Added RemoteSpeedTest example

 - fixed example testing script
 - Added finer axis ticks back in some instances
 - fixed improper bounds caching in log/fft mode
 - fixed exception handling in remoteproxy

  - reduced cost of transferring arrays between processes (pickle is too slow)
  - avoid unnecessary synchronous calls

Added RemoteSpeedTest example

  - AxisItem shows 2 tick levels instead of 3
  - Lots of boundingRect and dataBounds caching
    (improves ViewBox auto-range performance, especially with multiple plots)
  - GraphicsScene avoids testing for hover intersections with non-hoverable items
    (much less slowdown when moving mouse over plots)
These are deep changes; need good testing before we release them.

- Added documentation on export system
- Added flowchart documentation and custom node example

Bugfixes: 
- prevent PlotCurveItem drawing shadow when unnecessary
- deprecated flowchart.Node.__getattr__ -- causes too many problems.