Improvements in error handler for parser and tokenizer.

Don't use Object.error() in the tokenizer any more.  Add character
position information to the error messages in the parser and tokenizer.
Add support for hexadecimal (0xNNN) constants to tokenizer.
Move node CLI programs into bin/ directory.
Begin work on asm.js -> LLVM compiler.

Start by porting acorn (http://marijnhaverbeke.nl/acorn/) tokenizer
to TurtleScript.  This involved properly encapsulating the tokenizer
so that it is re-entrant, as well as lowering some syntax and replacing
regular expressions and switch statements with alternatives.