Add a basic logger interface

[modmuss50]

First stage of improving the log messages.

Has a slight breaking change to anyone who was passing a custom logger to the mixin extension.

[Player3324]

Potential additions might be categories and context objects (like affected ClassInstance etc) but this should be fine for now.

[modmuss50]

Potential additions might be categories and context objects (like affected ClassInstance etc) but this should be fine for now.

Yes, being able to specify class/method context is the next thing I want to do. It will be especially useful for the mixin remapping.