fmt: add support for goto

vlib/v/fmt/fmt.v

@@ -195,6 +195,12 @@ fn (f mut Fmt) stmt(node ast.Stmt) {
 			f.stmts(it.stmts)
 			f.writeln('}')
 		}
+		ast.GotoLabel {
+			f.writeln('$it.name:')
+		}
+		ast.GotoStmt {
+			f.writeln('goto $it.name')
+		}
 		ast.LineComment {
 			f.writeln('// $it.text')
 		}

vlib/v/fmt/tests/simple_expected.vv

@@ -3,9 +3,11 @@ fn hello() {
 	a = 10
 	a++
 	-23
+	goto lbl
 	b := 42
 	println('hello')
 	abc()
+	lbl:
 	if true {
 		a = 10
 		a++

vlib/v/fmt/tests/simple_input.vv

@@ -4,9 +4,11 @@ fn hello()
 	a = 10
 	a++
 	-23
+	goto lbl
 	b:= 42
 	println( 'hello' )
 	abc()
+	lbl:
 	if true {
 		a = 10
 		a++