Add unit testing

[Bilal2453]

Add unit testing for most methods. This is still working in progress.

This uses the Busted unit testing framework, running on Lua 5.4 (though it should also run on any Lua version).
The tests are ran from the main tree with busted -p .-%.lua tests/. The exact details may change in later commits.

Progress:

• ext_math
• ext_base
• ext_string
• ext_coroutine
• ext_table

[Bilal2453]

Busted expects a structure that looks like this:

└── spec
    ├── more_tests
    │   └── test_spec.lua
    └── test_spec.lua

(any .-%_spec.lua file inside a spec folder that is)

Should we use this instead of the current structure? All this would do is make it that we do busted to run the tests instead of adding and specifying the directory like busted -p .-%.lua tests/. We can also add a .busted file for various configurations including the patterns which would also effectively let you run busted alone.

[Bilal2453]

@truemedian Should be good enough for review! Do note the table/randomipair_spec.lua test currently fails as it is waiting merge of #27.

I changed how you run the tests, now all you need to do is busted in the root of the repository where the spec folder is located. I think the parts related to base tests are worth the review first, I am already debating rewriting those.

Also frankly, reviewing those tests is probably harder than writing them, may just want to give them a fast glance to assure nothing is severely out of place.