rename l_function method name

[GiacomoPope]

Fixes #210

[oscarbenjamin]

There isn't any point in doing this unless the docstring is updated to suggest calling the new function name.

I would do it like:

def l_function(self, s):
    """
    >>> l_function()
    123
    """
    ...


def l(self, s):
    """
    Alias for :meth:`l_function`
    """
    return self.l_function(s)

[GiacomoPope]

oh sorry, i just missed this

[oscarbenjamin]

I'm not sure it is worth changing the name here. I don't know much about this function and I don't know what it would normally be called. If the linter wasn't complaining then it would not have been suggested to change this so I would probably just leave it I think.

Putting "function" in the name seems sort of redundant when most methods are functions.

[GiacomoPope]

I think l_function makes sense, as it's a mathematical object known as a l-function (https://en.wikipedia.org/wiki/Dirichlet_L-function), obviously all the code is built with methods/functions but just calling it l doesnt seem very helpful to me. Happy to just close this though if you disagree

[oscarbenjamin]

Okay, let's get it in.