Add an "RSA key reconstructor" function

[unicornsasfuel]

It would be cool to have a function whose prototype is like:

rebuild_rsa_key(p=None, q=None, d=None, dp=None, dq=None, N=None, e=None, c=None, m=None)

It would step through a bunch of use cases to see if it could reconstruct the rest of the key. Mostly useful for CTF stuff, but would be nice once we have functions that could be used to recover a single factor or some such.