Refactor (new code) for clarity and ease of maintenance

[bobturneruk]

If we look at a line like this (it extends over several lines):

https://github.com/RSE-Sheffield/GPy/blob/801a72d7ea7f41862a963405860a00acdc294ef4/GPy/kern/src/lfm/lfmXlfm.py#L137

This probably began as good, pragmatic matlab code to get a job done. But in Python, it would benefit from a few changes such as:

• More easily distinguishable function names
• Limits to numbers of arguments to functions
• Excessively long lines