Lua: Ran several benchmarking tests

Performance looks very good.
- 8ms to create, configurate, draw 1000 circles
- 2ms to load 4 textures & build our whole scene

Lua: Added uptime() function that returns the uptime in seconds with at
least 4 decimal (milliseconds)
Lua: Added util.Benchmark(function, optional:amount)

Cleaned up some code