Rename overloaded operators (add underscores)

* add suffix unary operators
* add _! operator
* _._ and _&_ operator overloading
* allow calling function references with _! and access variables with _._
* rename . method operator to !
* various cleaning & improvements

Documentation will follow at some point.

test/tests/function reference chain call.ans

@@ -0,0 +1,13 @@
+$ fn
+	@1
+
+$ add(x)
+	@x+2
+
+:c = &fn
+
+{c!}
+
+{fn!add}
+
+{c!!add}