Added --show-variant-samples option to gemini_query

This which adds a column to the output listing all
samples containing a variant (HET or HOM_REF).
Added total, het and hom_alt columns to --show-variant-samples.
Added --sumarize option to stats.

--summarize plus a query will summarize the amount of het
and hom_alt variants each samples has returned by the query.
Added slightly less awful naming.
Added documentation for --show-samples and --summarize.
Formatting fix.
Formatting fix.
Merge pull request #147 from roryk/master

Added optional column of which samples have a variant to queries.
Merge pull request #152 from chapmanb/master

Fixes for reported installation issues
Update requirements.txt
[ISS #155] allow mixture of spaces and no spaces between select columns
Update requirements.txt

Make reqs.txt always pull from HEAD
[DOCS] add warnings about the diff b/w VEP and snpEff
Merge branch 'master' of github.com:arq5x/gemini
Add more useful error message if the database does not exist.
Merge pull request #158 from roryk/master

More useful error message for non-existant db in GeminiQuery
[ENH] support for genotype quals, ref_depths, and alt_depths.
[DOC] update docs for new gt_ref_depths, gt_alt_depths, and gt_quals columns
bump to version 0.4.0b
[DOC] add 0.4.0b to release history