Adding new PARALLEL option to unload

- Adds PARALLEL option to unload [Docs](http://docs.aws.amazon.com/redshift/latest/dg/r_UNLOAD.html?sc_ichannel=em&sc_icountry=global&sc_icampaigntype=launch&sc_icampaign=em_118617410&sc_idetail=em_1333791181&ref_=pe_411040_118617410#unload-parallel)
- Adds tests for parallel option
- Adds requirements.txt
- Fixes a few flake8 things

Signed-off-by: Jason Myers <jason@jasonamyers.com>