Add hash source support

This allows you to whitelist inline scripts by providing the hash values. There are some smarts here that will autoamtically compute hashes in dev/test and warn you if things are going to blow up.

A warning message is printed to the console if an unknown hash is mentioned.
don't load the hashes on every run
regex should use \s for whitespace
Load hashes once
consistent error message
add helper without a block
Revert "add helper without a block"

This reverts commit 4088e03697ff700ff7d0a2b9ebf39b31bf1def3b.
add nonced_style_tag too
remove some trailing commas
remove trailing newline
Merge branch 'master' into script_hashes_again

Conflicts:
	Gemfile
Merge pull request #121 from twitter/script_hashes_again

CSP level 2 hash integration