Add RDI submodule, port Kitrap0d

This commit is the first in a series that will move all the exploits that use RDI
over to the R7 fork. The RDI source will be in a single known location and each
exploit will have to work from that location.

The kitrap0d exploit has been migrated over to use this submodule so that there's
one example of how it's done for future contributions to follow.
Land #2698 Reflective DLL Submodule

Adds a Reflective DLL submodule in external pointing at the Rapid7 fork

Updates kitrap0d to use above submodule

Adds a make.bat file to create kitrap0d