introduce a new, more ergonomic syntax for haku
not all features are implemented just yet. still missing:
- custom tags (non-True/False)
- color literals
- lists
this fixes the case where
(def botsbuildbots (fn () (botsbuildbots))) (botsbuildbots)
would not run properly (return with a "set def index out of bounds" error)
also make exceptions store String instead of &'static str for better error reporting
closes#33