Support for relocation of RIP-relative instructions in `FunctionHook`

[alexrp]

This is quite a difficult problem to solve, but it is possible. Instructions that use RIP-relative displacements have to be rewritten to equivalent sequences using absolute addresses. The tricky part is picking a volatile scratch register to use in the rewritten code that won't conflict with the original code.

[alexrp]

Until this problem is properly solved, we could factor the displacements used in prologue instructions into our code placement. That should be fairly simple to do.

[alexrp]

This feature is a major undertaking, to the point that it will probably be the main theme of a major release. And that's assuming I ever get around to it...