Stub out bundle map/reducers
Bundle reduce steps
Concat to utf-8 buffer
Merge branch 'master' into bundle-map-reducers

Conflicts:
	lib/sprockets/bundle.rb
Extract reducers option to bundle
Merge branch 'master' into bundle-map-reducers
Merge branch 'master' into bundle-map-reducers
Merge branch 'master' into bundle-map-reducers

Conflicts:
	test/sprockets_test.rb
Add register bundle reducer
Merge pull request #627 from sstephenson/bundle-map-reducers

Bundle map/reduce