Only show early voting sites currently open.

Also show dates early voting sites open and close in map popup.  Closes #71.
Zoom in less far on map.

Closes #72.
Merge pull request #73 from flibbertigibbet/feature/early-vote-date-range

Only show early voting sites currently open.
Add instructions for deployment
Merge pull request #75 from flibbertigibbet/feature/doc-deploy

Add instructions for deployment
Merge pull request #74 from flibbertigibbet/feature/less-zoom

Zoom in less far on map.