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.
Please revert this to the original name, "IDEA".  "Alleged-RC4" came from the fact that RC4 was originally a trade secret and became public via an anonymous email with source code.  IDEA has no such colorful history, and this is the first time I've ever seen anyone refer to "Alleged IDEA".