Process semantics and abstraction problems on Linux, MacOS, Posix, Windows.

TODO motivation: audience/why this is actually relevant to read, ie security. This text documents process semantic differences between Posix, Linux and Windows regarding
  1. IPC.
    1. Signals.
    2. Pipes.
    3. Sockets
    4. Shared memory.
    5. Shared memory.
  2. Security.
    1. File access permissions.
    2. User permissions.
    3. TOOD.
  3. Process groups.
  1. IPC.
  2. Posix.
  3. Process groups.