don't use autoload; requires
reordered and organized bin/image_optim options summary
extracted checking access to bin
-s option of which command is custom and should not be used, closes #7
use `env` and `nice` commands + io redirection instead of forking and setting env, priority and reopening io using ruby methods, closes #8
v0.7.0
Merge branch 'toy-master'

Conflicts:
	lib/image_optim.rb
	lib/image_optim/worker.rb
try to account for dash in system call