User visible changes in `InterProcessCommunication`

Version 0.1.5

Fix definition of constants SIGUSR1 and SIGUSR2 (see PR 12).

Version 0.1.4

convert(RawFD, f) and RawFD(f) yield the raw file descriptor of FileDescriptor instance f.

Version 0.1.3

Argument readonly is now a keyword in ShmId constructor and shmid method. Old behavior where it was the optional last argument has been deprecated.
Argument shmctl checks that the buffer is large enough. Call IPC.unsafe_shmct to avoid this check or to directly pass a pointer.

Version 0.1.2

Export umask to set the calling process's file mode creation mask.
When creating a semaphore, Semaphore(...) ignores the calling process's file mode creation mask for the access permissions while open(Semaphore, ...) masks the access permissions against the process umask like sem_open.
Standard C types are no longer prefixed by _typeof_. For example, Julia equivalent of C mode_t is given by constant IPC.mode_t.

Version 0.1.1

Provide named and anonymous semaphores.
Provide shared memory objects (instances of SharedMemory) which can be associated with System V or POSIX shared memory.
Provide versatile wrapped arrays (instances of WrappedArray) which are seen as regular Julia arrays but whose elements are stored in a managed object.
Arrays in shared memory are special instances of WrappedArray whose contents are stored by an instance of SharedMemory.