Negative numbers, throw expression and print/ln name changes.

Fixed a major bug that prevented negative numbers from being seen as is. They were parsed like names, for example -1 would be a name instead of a number. This is because - is a valid name token, and numbers are allowed before letters and symbols.
Example: a-1 would be a valid name.

• Fixed -1 issue.
• println and print are now println! and print!, because they're impure functions and that makes it clearer.
• Added throw expression. Before that the only way of rising an error was to define externally Lua's error.

; Before update
(def-extern error)
(if some-condition
  (error "Yo"))
; Now
(if some-condition
  (throw "Yo"))