Use mabrek branch of epgsql.

This fixes a number of problems:

https://github.com/ChicagoBoss/boss_db/issues/57

and

https://github.com/ChicagoBoss/boss_db/issues/128
Fix for saving new boss records with an uuid as id to pgsql
Merge pull request #144 from synlay/feature/pgsql_saving_records_with_uuid_fix

Fix for saving new boss records with an uuid as id to pgsql
Fixes for a proper usage of redis as a caching server
and improvement of the README for clarification on
how to configure the cache_servers option correct.
Added missing terminate/1 callback
Close caching server connections on terminate
Merge pull request #145 from synlay/feature/redis_caching_adapter_fix

Fixes for a proper usage of redis as a caching server
Merge pull request #146 from synlay/feature/caching_adapter_terminate_tweaks

Added missing terminate/1 callback and cache_adapter_*:terminate tweaks
Merge pull request #143 from davidw/master

Use mabrek branch of epgsql.