fix evaluation of perl subs
add repr for Wat::Begin
better error reporting in env_bind
add map-list grep-list sort-list ref native calls
fix nil? to be robust to undef values
fail correctly on undef combiner
update for JSONY 0.0.8
store response from previous execution as _
overload cons cells to arrayify
intro get-current-environment as added to wat-js
add def method to Wat class
use def method to better handle _ val for repl