Bump to 2.0.0, Added nil return, added rockspec (#2)

* Added rockspec file
* Added rock build action
* Added explicit `nil` return
* Bumped to v2.0.0

sleep-2.0.0-1.rockspec

@@ -0,0 +1,21 @@
+package = "sleep"
+version = "2.0.0-1"
+source = {
+   url = "https://github.com/aziascreations/LuaJIT-Sleep/archive/refs/tags/v2.0.0.tar.gz",
+   dir = "LuaJIT-Sleep-2.0.0",
+}
+description = {
+   summary = "Pure LuaJIT bindings and wrappers for Win32 and Linux sleep functions.",
+   detailed = "Module that exposes millisecond and second precision sleep functions for Linux and Windows without having to compile anything.",
+   homepage = "https://github.com/aziascreations/LuaJIT-Sleep",
+   license = "CC0 1.0 Universal"
+}
+dependencies = {
+   "lua >= 5.1"
+}
+build = {
+   type = "builtin",
+   modules = {
+      sleep = "sleep.lua"
+   },
+}