Parse negative numbers

Author: viniciuslrangel

examples/scripts/forEach.mcscript

@@ -1,6 +1,6 @@
 #file: ./foreach
 # basic loop
-forEach(var i = 0; i < 10; i++){
+forEach(var i = -5; i < 5; i++){
     /say hey
 }
 

lib/parser.js

@@ -695,6 +695,13 @@ function parse_atom() {
         return tok;
 
       }
+      if (tok.type == "op" && tok.value == "-") {
+        let num = input.next()
+        if(num.type != "num") {
+          unexpected()
+        }
+        tok = { type: "num", value: -num.value }
+      }
       if (tok.type == "num" || tok.type == "str") return tok;
 
       unexpected();