add used_bins method to worker for preresolving
tell about disabling worker using an argument as well as using an option
extract Worker#wrap_resolver_error_message
add Worker#resolve_used_bins!
add Worker.create_all
extract BinResolver.collect_errors
remove creation of Abc worker in specs
add Worker.resolve_all!
increase Style/ClassLength to 150
Merge branch 'preresolve-bins'

Conflicts:
	lib/image_optim.rb