Merge pull request #18 from meteficha/use-cipher-aes-api

Use cipher-aes' API instead of using it via crypto-api.
Version bump
Use skein-1.0.*, major version bump to 0.9.

The new skein package implements a revised algorithm, which means
that clientsession 0.9 won't be able to verify cookies from
clientsession 0.8.
cipher-aes 0.2
cprng-aes 0.4
Remove unneeded line
Version bump
Fix for cipher-aes < 0.2
cprng-aes 0.5 support
Improve docs regarding security.
Bump version to 0.9.0.4.