refactor fetch_server to use sorted sets and support for least-connetions
refactor backend datastore to use sorted sets
get/set backend configs and set backend connections
Refactor to use score instead of specifically connections
use specific version of lapis for travis
[travis] only test master branch
Update readme [skip ci]
misc tweaks
update CHANGELOG
Merge pull request #4 from rstudio/feature/least-connections

Load balancing based on score.