Rework windows API

[dobin]

Currently there are two or three windows APIs used:

• arch_windows.c: Reflexxion system calls stubs (direct syscalls)
• inject/: from go-inject, to perform process injection
• syscalls/: from sliver, to perform sliver related stuff like donut shellcode injection

At least merge inject/ and syscalls/. Preferable replace with direct syscalls in pure go, if possible.