Factor out TurtleScript standard libary (from binterp into new stdlib module).

A bunch of related changes to places which make new binterp contexts,
including bin/repl.js (which now puts the standard library into the REPL
context).
Make write-rust-* into proper TurtleScript; add version to package.json.

write-rust-bytecode.js still has a regexp, which makes it not proper
TurtleScript, but it's closer now.

bin/parse.js does a reparse of the jcompiled source, which just verifies
that jcompile is now broken.
Documentation updates: format many modules for 'docco'.

Fixed up some of the browser-based demos/test cases while I was at it.
Update README.