Use consistent snake_case variable names

[krisgesling]

Just going through a PR and there are camelCase variable names sprinkled through out the code base. Would be good to move to the Python standard snake_case for the whole repo.

The challenge will be anchorDate as it's used in a public method and hence by downstream users. Will need to deprecate it and support that kwarg for some period of time.

[ChanceNCounter]

anchorDate becomes a little tricker still in that it's probably passed positionally in a lot of places. Deprecation works the same way it ever would, but it's mildly cruel, in that the new name has to go on the end first, then jump to the front.

def function(var1, deprecatedVar, var3, var4, renamed_var):

throws a deprecation warning on deprecatedVar for a few months or pending a "breaking" version number. Then, it becomes

def function(var1, renamed_var, var3, var4):

I don't think there's a better way, but it's always an awkward change.