better interpretation for "and/or"
an improved interative repl interface

* support for lambda beside string as revi's prompt
* auto tab completion based on global variables
* friendly notification for users who don't know how to exit
Improved syntax rules for single expressions

The main purpose is for cope with the problem it made for built-in
user-defined functions that the old syntax regards 0..inf expr(s) as a
common multiple expressions.