initial attempt at modular src code

the plan is to use a technique described in Patrick Lee's
<em>CoffeeScript In Action</em> to create a single .js file
to be included by the webpages to mirror the behavior of
a single source file (since browsers don't support modules)
forgot to add these, whoops
trying to work with stitch
make "modular" system work

the cake file now uses a bash script to concatenate all
*.coffee files in the source directory into a file called
build/Greenhorn.coffee. After that's done, the coffee-script
compiler is used to make lib/Greenhorn.js from build/Greenhorn.coffee

the new src/index.txt file is used to specify the exact order in which
files should be concatenated. This file prevents dependancy errors
at runtime, such as the TextBox class not knowing what a Sprite is.