Better ruby engine support

Removes support for 1.8 rubies (MRI, Rubinius, JRuby)
Test support for Rubinius 2.1 & 2.2, JRuby in 2.0 mode

Add puma and postgres for all engines

Better support alternative ruby engines by not including Gemfile.lock in
version control and including more pessimistic dependency versions.
Includes new ey.yml option to not warn about missing Gemfile.lock