made everything compile to a single apl.js file

Coffee files are included in apl.coffee by name in the correct order.

The CommonJS module system is dismantled and the top-level variables in
modules are essentially global variables.

An implementation of the Γ function was inlined, to avoid dependency on
an external library.

Doctests pass at this point, but the web demo and the CLI aren't
functional.
trimmed down CLI and made lib/apl.js executable

I set the first line of lib/apl.js to

    //usr/bin/env node "$0" $@ ; exit $?

which should make it work both as a JavaScript module and as an
executable shell script.

The command line interface is now at its bare minimum: it can run APL
scripts from a file/stdin or launch a REPL.
web demo works
mobile demo works
removed build script for downloads/*