preliminary support for builtin functions, various fixes, various tweaks

cmd/tools/builders/go_builder.v

@@ -0,0 +1,7 @@
+module main
+
+import v.builder.gobuilder
+
+fn main() {
+	gobuilder.start()
+}

cmd/tools/builders/golang_builder.v

@@ -1,7 +0,0 @@
-module main
-
-import v.builder.golangbuilder
-
-fn main() {
-	golangbuilder.start()
-}