Support starting server on background

[mkorpela]

The init currently calls serve_forever() that prevents execution from continuing.
Init also registers signal handlers - this is only allowed in the main thread.
Thus currently it is not possible to start the server on background and continuing working on something else on the main thread.

[pekkaklarck]

Yeah, this is stupid design. Shouldn't be too hard to fix,

[pekkaklarck]

Turned out to be much more work than I anticipated but ought to be pretty much ready now.

@mkorpela do you have time to test this and perhaps also to review the code?

Functionality is documented in the README and also in docstrings in the code. Documentation comments are obviously appreciated too.

[pekkaklarck]

This ought to be now supported and 1.1 RC 1 is also out. Testing the functionality and reviewing the related documentation in the README would be highly appreciated.