[perl #36330] [TODO] Create a BigNum PMC

[Andrew Whitworth via RT]

Current status:

1) I have ripped out src/bignum.* a while back. There were no major
complications from this.

2) I added a stub BigNum PMC to the repo that was based on the existing
BigInt implementation. rurban++ has been working on it to get it working
and properly tested. Others have been contributing fixes along the way.

I am calling this ticket resolved now. We can follow up with any related
issues at trac.