write relativistic notebook

[rccreswell]

Closes #18

[MichaelClerx]

Hey @rcw5890 ,

I updated to the new syntax and re-ran. Results are a bit different though: better for some, worse for others. I don't think this is due to any changes I made:

• Old test file: https://github.com/pints-team/pints/blob/f1f3fda5f3c3f8fd23b228a7a4fbf0e4dbc659fa/pints/functionaltests/relativistic_mcmc.py
• New test file: https://github.com/pints-team/pints/blob/issue-1294-functional-testing-module/pints/functionaltests/relativistic_mcmc.py

So maybe need some more iterations here and there?

(I also switched off the log printing, as Ben requested)