Update function documentation to use luadoc format

[mindfilleter]

This will permit us to automatically generate documentation to include in the project's wiki from the source.

Documentation for the format is here: https://keplerproject.github.io/luadoc/manual.html#introduction

It's not much different than what the lib already does. Here is an example:

--- Call the function fn and assert that an exception is thrown with
--- the given `expected message`
-- See `test/test_test.p8` for examples of how to use this assertion
-- @param fn A function to be called
-- @param expected_message The exact text of the expected exception
-- @return nil
function TestCase:assert_throws(fn, expected_message)
   local threw = false
   if (expected_message == nil) expected_message = ""
   try(
      fn,
      function (e)
         threw = true
         local err_msg = self:_parse_error_message(e)
         if err_msg ~= expected_message then
            assert(nil, "expected exception '"
                   .. expected_message .. "' but received '" .. err_msg .. "'")
         end
      end,
      nil
   )
   if not threw then
      assert(nil, "expected exception '" .. expected_message .. "' but none was thrown")
   end
end

[mindfilleter]

I would suggest adding "help wanted" and "newbie friendly" tags to this

[sparr]

-- @tparam string text this parameter is named 'text' and has the fixed type 'string'
-- @treturn {string,...} a table of substrings

[sparr]

I've pushed changes to some comments to this format. Still a lot of existing comments that need updating. If anyone decides to tackle this, please comment before you start so we don't step on each others' toes.

[mindfilleter]

Thanks for doing this. I've done some research on getting ldoc working. I'd like to discuss my findings with you. Are you on any of the discord servers?

[sparr]

I'm on the one linked from the README in this repo ;)

[sparr]

Done in #9 and https://github.com/sparr/pico8lib/commit/678c714f8518c79f77322a05fc53e23014eefc3d