Add external description priority.

1) Find go:description tag.
2) Find meta description.
Add external favicon priority.

1) Find go:image tag.
2) Find rel icon.
3) Find item prop as image.
Add external images from the entire page.
Add external description priority.

1) Find go:title tag.
2) Find meta title.
Add active support gem
Add parser specs
Add Page subclassing to represent the page as a resource.
Add the basic usage for now.