Merge pull request #11 from jabr/specify-environment

Specify the environment for eb:show_config and eb:deploy tasks
Fixes #12.  This allows the optional use of RAILS_ENV or the :environment argument.  Updated docs accordingly.
oops, forgot to re-enable deployment after testing rake argument resolution
changed ruby version
make sure the lockfile is ignored
extracted config base and moved to a separate gem 'dry-config' for reuse elsewhere.