Remove evals() when resolving model functions (i.e. kernels, likelihods, etc.)

[hadsed]

Instead make it so that the function pointer looks something like:

covFunc = kernels.spectral_mixture

that way it's clear where the function is defined and coming from.

[hadsed]

https://github.com/hadsed/PyGPML/blob/master/gaussian_process.py#L37

[hadsed]

6e4e160