more pass by references, set err_expr only when necessary

readline's handling of multiline input improved

see: http://arclanguage.github.io/ref/filesystem.html

more constness

example:
(= a '((1 2)))
(macex '(= (caar a) 3)) ; => (do (scar (car a) 3))
(= (caar a) 3)
a ; => ((3 2))

v0.23: closure source form is printed

multiline strnig supported in REPL

constness

fixed int (round)

pipe-from