Add Student's t-likelihood function.

I've added a Student's t-likelihood function and a set of tests for it in likelihood_tests.py.

Refs #157 (closed).

mentioned in issue #157 (closed)

mentioned in merge request !144 (merged)

added 27 commits

• e8566478...36378a6a - 20 commits from branch Monash:master
• b86135a5 - Add an exponential distribution lieklihood function
• ac3846c2 - likelihood.py: Fix doc string for exponential likelihood
• 55a7c442 - Add exponential likelihood to the documentation
• 9346532b - likelihood_tests.py: add tests for exponential likelihood
• 7a236c62 - likelihood_tests.py: minor tidy up of exponential likelihood tests
• 29511c80 - Merge branch 'master' into exponential_likelihood
• f3a9d27a - Merge branch 'exponential_likelihood' into studentt_likelihood

Compare with previous version

I've merged this with !144 (merged), so if !144 (merged) is merged with master first then this should be able to merge without conflicts.

approved this merge request

merged

mentioned in commit a0f94db4