support string return values from ffi functions

this is most likely not enough, because we must free the result?
implement '/' and '*'

this also improves '+', it doesn't do an initial addition to 0 if it
isn't necessary.
fix octal literals, add some tests for numbers
move repl banner inside repl fn
initial batch mode and cmdline args

the argument parsing is not very sophisticated, but then why should it
be?
add -e|--eval option
support reading code from stdin
use batch mode in makefile
Merge pull request #22 from heyLu/num-improvements

num improvements
Merge branch 'batch-mode' of git://github.com/heyLu/pixie into heyLu-batch-mode
fixed translation via some odd compiler bugs
fixed the odd compiler bug with range
support ';' comments
ignore compiled binary
added shallow continuations
working on generators jit stuff
remove the force_virtualizable hint, it now translates, but why?
Merge pull request #24 from pixie-lang/generators

Generators
benchmark files, and fixes to the compiler for empty hashmaps
example implementation of mu-kanren, added a few functions to stdlib