Implement extended set options added in Redis 2.6.12.

SPECS :
- http://redis.io/commands/set
- https://github.com/antirez/redis/issues/931
Implement extended set options added in Redis 2.6.12.

- support Python 3.x
Implement extended set options added in Redis 2.6.12.

- fix wording/formatting
finer grain tests
pep8
testing redis version on travis
travis runs 2.6.12, great.
tests should pass on older redis versions
pep8 testing on travis
testing travis-ci pep8 integration
attempting to add a separate build for pep8
remove matrix, doesn't seem to work
more weird pep8 travis hacking
bash foo
install pep8 in install: section
run fewer pep8 builds
remove offending pep8 line, travis ci should pass now
Adding incrby alias
Merge pull request #343 from cypreess/master

Fixing INCRBY inconsistent naming
rst format readme