sort: sorting algorithms and support for sorted data structures

The sort module provides functions for sorting slices, as well as operations on
sorted slices, such as binary search.

The functions [[sort]] and [[search]] are provided for working with generic
slices. In order to work with a user-supplied slice of an arbitrary type, the
slice must be cast to []opaque and the size of the member type passed alongside
it (e.g. size(int)). The functions also take in a [[cmpfunc]] argument, which is
called to determine how the slice items should be ordered.