Update abstract.

The license is explained in detail in the paper, but there is no reason
readers should have to go past the abstract to know what the license is.
Simplify initial intro paragraph
Remove some y-ticks from histogram
Justify Python after introducing it
Emphasise FOSS importance for modification
Minor edits
Describe 'np.histogram' in figure legend
compute -> perform, like -> such as
Add wrapup for getting started section
Rewrite data format/pipelining, add Mahotas reference
Homogenize references in introduction
Homogenize references to match introduction.
Minor fixes to development practices section
Merge pull request #51 from jni/copy-edit-dev

Copy-edit the development practices section
Minor readability fix suggested by @sciunto
Minor edits to text and refs in research section
Make lesion figure wide
Merge pull request #52 from jni/copy-edit-res

Minor changes to research section
Tweak usage-education, add science fair example
Homogenize numpy mentions, oops, NumPy ;)