Fixed browser back button and miscellaneous changes

[JasonStoltz]

Fixes #21

Browser Back button followed by Forward button wasn't properly working.

To reproduce:

• Perform a text search
• Make a facet filter selection
• Press the back button
• Press the forward button
• Note that pressing the forward button will not reapply the filter, as it should.

Also backfilled some more useful behavior:

• mapContextToProps
• Support "sort" as a valid facet parameter

Also added deployment instructions to the README. Be sure to run through them and make sure they work!

Added CircleCI.