Documentation for .register() method, plus let it accept a name

[simonw]

The method currently looks like this:

asyncinject/asyncinject/__init__.py

Lines 21 to 25 in fd5ef10

	def register(self, fn):
	self._registry[fn.__name__] = fn
	# Clear caches:
	self._graph = None
	self._reversed = None

This isn't yet documented. Also it would be neat if you could do this:

registry.register(lambda x: x.upper(), name="upper")

If name= is not provided it can default to fn.__name__.