Camellia support

* Tests for CBC, OFB, CFB, and ECB
* Tests will be automatically skipped if camellia support is not present in your OpenSSL library (e.g. OS X 10.8 with default OpenSSL)
* tox will display skip reasons
* supports method in api (for skipif tests)
* Test for unsupported cipher in create_block_cipher_context
* Docs for the cipher