Support wire-time min/max_wirings override?

[tmontes]

Idea from #43:

For full instantiation-time, per-callable and wire/call-time settings consistency, this could be supported:

w = Wiring(max_wirings=1)

w.some_callable.wire(...)
w(max_wirings=None).some_callable.wire(...)         # would otherwise fail

Other than consistency, I fail to find how this will be useful. Would it?