Keywords need to be part of the function signature

[mscuthbert]

It's time to stop creating methods and classes like this:

def __init__(self, **keywords):
     if 'hello' in keywords:
         hello = keywords['hello']
     else:
         hello = 'hi'

All the keywords expected by a method should be in the function signature:

def __init__(self, *, hello='hi'):

It's still okay to allow a generic **keywords argument, if the class is expected to be subclassed by something with more keywords or if it calls a subfunction that might have more keywords:

def __init__(self, *, hello='hi', **keywords):
      super().__init__(**keywords)
      self.hello = hello

But it's not at all apparent to a user what is possible with **keywords in the current state.

Do this before (or start it) as part of #763 show implementation.