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
Minor readability fix suggested by @sciunto
Homogenize numpy mentions, oops, NumPy ;)
Our algorithms are sophisticated, not just quite sophisticated
Separate adjectives with a comma
Merge pull request #50 from jni/minor-edits

WIP: Minor edits