Merge branch 'refactor' into config
unused instead of unknown in message in assert_options_empty!
read config from image_optim.yml at XDG_CONFIG_HOME (~/.config by default) and from .image_optim.yml in cwd
don't mess specs with global and local config
Merge branch 'refactor' into config

Conflicts:
	lib/image_optim/config.rb
specs for reading global and local config
configuration section in readme
configuration note in bin help
Merge branch 'refactor' into config
don't allow failures with jruby
Merge branch 'master' into config
global options in readme
Merge branch 'config'