Remote reg and pub/sub

[uwiger]

First sketch of remote registration and gproc_ps subscriptions.

The idea is that registering remote pids shouldn't be a problem in itself, but all regs must go through the gproc server, can only have local scope, and the API function should be distinctly only for non-local pids.

TODO: add ensure_... and unreg functions etc. as well as test cases.

[uwiger]

• Added tests for the remote API.
• also added some pub/sub test cases
• fixed dialyzer config and warnings
• fixed some documentation issues

[uwiger]

Also fixed some return values in gproc_ps, mainly regarding 'singles'. They now match the documentation.