have sprockets add images directory when looping through asset try_paths
map images_dir to Middleman sprockets
add missing append_path for images_dir
added response code step to server_steps
cucumber test coverage for sprockets images
updated extension to take :assets_load_paths config param with hash of paths and mapping for sprockets
cucumber tests for custom assets load paths
renamed assets-load-path fixture and move feature test to sprockets_gems.feature
merge branch 'custom-load-paths'