Added the ability to pass multiple arguments to a script

this is done by treating any arguments between the initial string and
the callback as an array which can have any number of elements
add ability to return multiple arguments from a script

this is done by returning non-error arguments via the bridge as an array
updated readme
streamlined result vars passed back from bridge

there's now no "err" event that the bridge emits, it just emits "output"
and follows the convention of using the error as the first argument
Merge branch 'variable-arguments'
bump to version 0.2.1