Provide some tests

[vhaasteren]

Provide some simple tests for the sampler

[vhaasteren]

The examples folder now contains a "gaussian_likelihood" and a "curved_likelihood" jupyter notebook. The Gaussian likelihood also contains a simple transformation class that transforms away an interval for usage with Hamiltonian samplers.

Questions:

• what other examples do we need?
• do we want to incorporate the interval transform as functionality inside of the PTMCMC package somewhere? Perhaps as a module? It is a very general thing.

[jellis18]

Finally added a simple example for an N-D gaussian without using the hamiltonian sampling. This also shows how to add custom jump proposals. We still may want a parallel tempering example