Some more core lisp functions
(letrec) functionality added
Variadic function calls
More common lisp functions
docstring
Show expr that caused evaluation exception
First expr in an S-expr can be evaluated
Tidy line spacing
Set parse actions
Wrong indent level
Moved converters into utils
Brand AST primitives with the source/location - for error handling;
Fix bug in call, where formals > args doesn't raise error