[pal] PAL is Poorly Organized

[BrianZill]

Context

Currently, the PAL is organized by type of thing being abstracted: constant, function, structure, etc. And/or by platform (there currently is a linux subdirectory).

Proposed Solution

The PAL should be organized by module: e.g. sockets, shared memory, cpu architecture, etc. With each file organized by thing being abstracted, NOT by the platform. The platform should be the lowest level.