Update rebar.
Update dependencies.
Add a benchmark for concurrent map updates.

Update a series of maps representing teams which are computed from
cumulative updates to a series of individual player scores.  Add and
remove members of the team, while concurrent score changes are
occurring.
Merge pull request #131 from basho/feature/csm/teams

Add a benchmark for concurrent map updates.
Remove non-core modules
Dialyzer -Wunmatched_returns fixes