New class and command-line script to find heterozygosity separately for high/low MAF
Separate functions for computation and text/json output
Use new runJson method
Add test for MafHetFinder
Add option for text output on command line, and update README
Added het_by_maf.py
Merge pull request #6 from iainrb/devel

Added MAF/het calculation for release 0.3.0