Feature/#230 xpath (#322)

* Implemented XPath for CDP driver

* Added XPATH function

* Added e2e tests for CDP

* Fixed linting issues

* Added support of XPath to HTTP driver

* Fixed linting issues

pkg/stdlib/html/xpath.go

@@ -0,0 +1,31 @@
+package html
+
+import (
+	"context"
+
+	"github.com/MontFerret/ferret/pkg/drivers"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+)
+
+// XPath evaluates the XPath expression.
+// @param source (HTMLPage | HTMLDocument | HTMLElement) - Target HTML object.
+// @param expression (String) - XPath expression.
+// @returns (Value) - Returns result of a given XPath expression.
+func XPath(ctx context.Context, args ...core.Value) (core.Value, error) {
+	err := core.ValidateArgs(args, 2, 2)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	element, err := drivers.ToElement(args[0])
+
+	if err != nil {
+		return values.None, err
+	}
+
+	expr := values.ToString(args[1])
+
+	return element.XPath(ctx, expr)
+}