Release 0.5.0.0 : large performance improvements

This release sees one large change:

• The pandoc-plot executable will now process documents in parallel. This should dramatically speed up processing of large documents with lots of figures. This happens automatically through the function plotTransform.

Other small changes:

• Added a benchmarking suite.
• Added defaultConfiguration so that people don't have to install the data-default package to get access to default configuration values.
• Added a check for the matplotlib toolkit, preventing users from using matplotlib.pyplot.show in figures. This would halt pandoc-plot.