updating readme to reflect using PyCrypto instead of gpg for symmtric encryption
add pycrypto as a dependency
renaming "passphrases" to "keys"
split misc functions into helpers module
fixed test after refactor
refacted to move the encryption/decryption into SuperCipherFile class
moved cleanup code into __del__ in SuperCipherFile class
less verbosity while compressing file
updated test to rely on SuperCipherFile's cleanup
use only PyCrypto ciphers, and refactor stretch_passphrases to make keys the correct lengths
refactor to encrypt with PyCrypto instead of GPG
replace gpg symmetric encryption using 3des, cast5, blowfish, aes256, twofish, camellia256 with PyCrypto and only cast5, blowfish, and aes256
removing symmetric functions from gnupg, and made new symmetric crypto catch bad passphrase errors
fix test_scfile_decrypt_invalid_archive test by adding new test data
remove gpg symmetric tests, since gpg symmetric code has been removed
fix test_scfile_decrypt by adding new test data
add invalid passphrase test again
update design document based on switch from GPG to PyCrypto
use PyCrypto's Random object to create the salt
fixing more things related to removing helpers.get_random