Feature/#33 wait class function (#63)

* #33 Lib cleanup. Added WAIT_CLASS and WAIT_CLASS_ALL functions

* #33 Fixed attr update

* #33 HTMLElement.WaitForClass

* #33 Updated HTMLDocument.WaitForClass

pkg/stdlib/html/inner_html.go

@@ -0,0 +1,38 @@
+package html
+
+import (
+	"context"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+)
+
+/*
+ * Returns inner HTML string of a matched element
+ * @param doc (Document) - Parent document.
+ * @param selector (String) - String of CSS selector.
+ * @returns (String) - Inner HTML string if an element found, otherwise NONE.
+ */
+func InnerHTML(_ context.Context, args ...core.Value) (core.Value, error) {
+	err := core.ValidateArgs(args, 2, 2)
+
+	if err != nil {
+		return values.EmptyString, err
+	}
+
+	err = core.ValidateType(args[0], core.HTMLDocumentType)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	err = core.ValidateType(args[1], core.StringType)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	doc := args[0].(values.HTMLDocument)
+	selector := args[1].(values.String)
+
+	return doc.InnerHTMLBySelector(selector), nil
+}