Lighting proof of concept

Sometimes I find it nice to do a 'fun' item off the list every so often, even if it's not really essential/called-for. 

Lighting is fun to mess with (especially colour cycling), and I'm a big fan of day/night cycles and the atmosphere they create etc. so I just wanted to do a proof of concept of what would be required to get it to render properly

It's a very quick test and it's 'fake' (it's sprite colour+alpha modulation, so no real shadows) - but it's nice to see it's not that hard to make this kind of work. Because each light is just a tile from the spritesheet, it would also be possible to animate lights once I have animated sprites too.

(If you look very closely you might able to make out the UI elements visible in the top left too - they need separating from the world draw pass so they don't get affected by light/darkness)