Dev

[danielward27]

Bunch of things, most notably:

• Error on nans (instead of sometimes dropping)
• Add check_k for checking for reasonable basis dimension.
• Add a hexbin plot for visualising residuals in 2d.
• Add method for plotting random effects (qq-like)
• Centralise the rpy2 imports of r packages. This significantly speeds up the import times, which were beginning to become cumbersome.