Merge remote-tracking branch 'canonical/next'

* canonical/next:
  fix nasty bug that didn't let relcool output errors
  make the default output _rel instead of relcool_output
  allow a user to specify additional opts to erlexec
  add examples of simple and complete relcool configs
  make sure ebin is removed on clean
  add inadvertantly deleted relcool.app.src
  support travis CI in relcool
  cleanup the rebar config
  remove docs (they have been moved to the wiki)
  all relcool to symlink in 'overridden' apps
  rcl_prv_discover now supports setting up 'link' type app_info messages
  support specifing overrides in the configuration
  support a new 'link' field in rcl_app_info
  minor cleanup and refactoring for rcl_prv_assembler, rcl_prv_discover
Merge pull request #22 from ericbmerritt/next

support the discover task searching the output dir
Merge pull request #23 from ericbmerritt/next

support release discovery in relcool along with app discovery
make all grabs deps if deps dir does not exist
fix: replace COnfigFile with empty string if undefined
fix: specifying config file as argument no longer crashes
Merge pull request #26 from tsloughter/next

make all grabs deps if deps dir does not exist
Merge pull request #27 from ericbmerritt/next

lots of bug fixes
Merge pull request #28 from erlware/next

Next
bugfix for empty configs in the Erlang API
move discovered releases to their own area of the relcool state