Reintroduce Alleged IDEA

All the patents on IDEA have now expired. The trademark on the name remains, hence "Alleged IDEA". This pull request is based on the original IDEA code from dlitz/pycrypto@v2.0.1 which was removed in dlitz/pycrypto@v2.1.0alpha1.

All tests pass as expected.
This is misleading.  Yes, IDEA has been examined, and it's known to be vulnerable against plaintext-recovery attacks, which are feasible after an expected 2^32 blocks due to its 64-bit block size.  See https://eprint.iacr.org/2012/623