Fix bug: crypto.Decipher#update() returns string, not void
Add buffer methods to crypto.Cipher and Decipher

See http://nodejs.org/api/crypto.html#crypto_class_cipher
and http://nodejs.org/api/crypto.html#crypto_class_decipher

for details.
Merge pull request #2925 from jjeffery/crypto_buffer_api

Crypto buffer api