Add unit tests for critical functions

[DeaglanBartlett]

As of commit 5ea089b5390cc6752cf66a38f99e09749af1196a, we have:

• Added some units tests based on the examples given in the tutorial
• Setup Github actions to run unit tests
• Added badges giving status of unit tests and coverage

Currently the coverage is only at 68%, so this needs to be increased so that all the code is tested. The sophistication of the tests can also probably be improved.

[DeaglanBartlett]

As of commit 8fd0612ddf81ee6d325bb5206a384fd957ab6ac1, the coverage is up to 85.55%

[DeaglanBartlett]

roxy.mcmc now fully covered as of 389b653c69c04f4f3b0ec54f1c63c16420c313a6 and the overall coverage has been increased to 94.53%

[DeaglanBartlett]

Commit 5e134bd655ee50f678732e5f3cfb0fc1baee34be increases the coverage to 97.27%, leaving 21 lines of code currently not covered by the unit tests.

[DeaglanBartlett]

Commit de5a633f1cfd07a1844640c40d9e1ed1713a02ce increases coverage to 99.61%. The remaining test to add is for the lines containing plt.show() in roxy.plotting.

[DeaglanBartlett]

Commit 7052ae7e078f6a88707a5994eb2682342e94dfac brings the coverage up to 100%. Although the sophistication of the tests may change with time, I will now close the issue as the original objective of adding unit tests for critical functions has been completed.