Implement predict_function_rva by ordinal

[ncatlin]

The 'create PE from scratch' guide describes a function to get the IAT address of imported functions.

Once needed libraries and functions are added to the binary, we have to determine their addresses (Import Address Table).

For that, we can use the predict_function_rva() method which will return the IAT address set by the Builder:

Binary.predict_function_rva(self, library: str, function: str) → int

However, this feature does not work with functions imported by ordinal, which causes problems with some common libraries like WS2_32.dll which tend to have their exports imported by ordinal (eg. by sysinternals tools).

I needed this functionality in the python binding, so here is the implementation with Python API support.