Takers wanted - BigInt/BigNum

[Leopold Toetsch]

The BigInt PMC has a lot of unimplemented MMD and vtable functions. Some 
are denoted with internal_exception ... "unimp", some are probably just 
missing.

So it'll be great if some folks could complete that.
A second job what be to take a start at an internal implemenation of the 
BigInt / BigNum stuff. The code in types/bignum.c is rather complete. It 
just needs to be hooked into the class code.

Thanks,
leo