syntax: 'var'->'let' 'function'->'func'

- 'var' has some weird scoping connotations with users of JS. better to change it to 'let', which will decide whether to make the variable a local or a global
- 'func' looks visually appealing lol
- some minor refactoring done in cparse.c

examples/iterator.cosmo

@@ -1,14 +1,14 @@
 proto Range
-    function __init(self, x)
+    func __init(self, x)
         self.max = x
     end
 
-    function __iter(self)
+    func __iter(self)
         self.i = 0
         return self
     end
 
-    function __next(self)
+    func __next(self)
         if self.i >= self.max then
             return nil // exit iterator loop
         end