context: add a new context module, based on Golang's context, intended to be used in webservers (#9563)

vlib/context/empty_test.v

@@ -0,0 +1,19 @@
+module context
+
+fn test_background() {
+	ctx := background()
+	assert 'context.Background' == ctx.str()
+	if _ := ctx.value('') {
+		println('This should not happen')
+		assert false
+	}
+}
+
+fn test_todo() {
+	ctx := todo()
+	assert 'context.TODO' == ctx.str()
+	if _ := ctx.value('') {
+		println('This should not happen')
+		assert false
+	}
+}