code cleanup & new content?!

i've split the game's codebase to files & functions. previously everything was in main.lua, but it was getting pretty bloated.

the main update & draw functions are looking pretty spiffy now:

you can peruse the code at https://github.com/verysoftwares/interobg

also, i've added the 4th, 5th & 6th circuits. the 4th circuit features homing bullets, the 5th is all about shapes, and the 6th has persistent bullets that keep you inside a circle.

hope you enjoy the visible & invisible changes!