Adding util functions for sharing memory between processes

[BrunoPujos]

Hello,

So this PR contains a few functions for helping to share memory between two processes. This require PR #21 for having some of the function needed.

A function get_shared_mapping already exist (https://github.com/hakril/PythonForWindows/blob/master/windows/utils/winutils.py#L511) so this may not be needed or maybe this has to be merged. The code is quite similar, one of the problem of the implemented get_shared_mapping is that, because the handle is not returned, it cannot be closed later on.

If this is not helpfull fill free to ignore.