ARC4 support
add ARC4 keysize testing
Merge branch 'master' into arc4-support

* master:
  Typo
  Be really explicit about what's good and bad
  Mention return types.
  Consistently use e.g.
  Module documentation.
  Single space.
  Add a new Mode interface to document mode.name and start on some prose docs for interfaces.
  Proper name for the iv thing.
  Actually note the properties for cipher modes types on their ABCs.

Conflicts:
	docs/hazmat/primitives/symmetric-encryption.rst
update docs to include arc4 example
Merge pull request #214 from reaperhulk/arc4-support

ARC4 Support