Add mmap, shm_open and other mman relatives

Add various wrappers to make interacting with Rust a bit more pleasant
for memory management.

Additionally, provide ftruncate(2), which is useful when working with
shared memory.

Allow managing CPU affinity of a Rust Task living in a system thread.
Merge pull request #13 from 12sidedtech/master

Add Memory Management and Scheduler Management Primitives