Provide LSP-friendly documentation file

[Andrey Proskurin]

Hello,
at the moment your language server won't give you helpful diagnostics and autocompletions because luasdl2 is a simple dynamic library that doesn't know anything about C comments. sumneko/lua-language-server has the concept of "libraries" to provide autocomplete and documentation for native C bindings.

Below is a tiny sample that documents SDL.init. I propose to provide such definitions for everything inside luasdl2. The only problem is that somebody would need to redo all the comments inside C source files to include type information for parameter and return values.

---@meta
local SDL = {}

---@enum SDL.flags
SDL.flags = {
	Audio = 16,
	Events = 16384,
	Everything = 62001,
	GameController = 8192,
	Haptic = 4096,
	Joystick = 512,
	NoParachute = 1048576,
	Video = 32,
}

---@param flags SDL.flags[]
---@return boolean # True on success or false
---@return string  # The error message
function SDL.init(flags) end

return SDL