Ruby wrappers for XND, ndtypes and gumath.

Since the xnd project is still in a development stage, the commits that these repos match are as follows:

• xnd: https://github.com/xnd-project/xnd/commit/05c3c177b1a5842681310e1c234091323a4e0cac
• gumath: https://github.com/xnd-project/gumath/commit/a20ed5621db566ef805b8fb27ba4d8487f48c6b5
• ndtypes: https://github.com/xnd-project/ndtypes/commit/c3c606710d8f711b33850a950079d75c20f87c2e