move function into appropriate module
dict:

 - tests
 - fix bug
 - improve error messages
 - new methods -- `keys`, `values`, `items` -- for accessing items as collections

set:

 - new methods `keys`
redo groups of CST node types

 - full implementation, in 1 module
 - split off `clojure` into new group by itself

add `_end` key to CST nodes -- line/column after its last character
use Dict instead of plain object where appropriate
style changes to satisfy jsHint
0.0.9