Add a pre-commit hook for running Prospector

[Dunedan]

This adds a pre-commit-hook for running
Prospector against all changed Python files of a git commit.

[coveralls]

Pull Request Test Coverage Report for Build 647

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.4%) to 77.234%

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Files with Coverage Reduction	New Missed Lines	%
prospector/exceptions.py	1	85.71%
prospector/message.py	1	77.97%
prospector/tools/pylint/linter.py	1	61.76%
prospector/encoding.py	1	61.11%
prospector/tools/init.py	1	96.15%
prospector/run.py	3	71.43%

Totals
Change from base Build 637:	-0.4%
Covered Lines:	1530
Relevant Lines:	1981

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💛 - Coveralls

[carlio]

I do like this, I use pre-commit all the time.

One request - could you add to the docs / README how to use it? There are lots of configuration options and in fact an old issue related to this - #56