Make initialisation more like bounding

[MDCHAMP]

I was really pleased with the bounding strategy changes, and I think that would be beneficial to have initialisation work in a similar way.

Should have:

• default class method of optimiser that calls a static method bound to an attribute
• overwritable by the end user or by inheriting optimisers
• init strategies to include as defaults: uniform, normal, fixed
• Include the new functionality in the readme

Should be an evenings work to write up and test.