#197 Fixed meta tags may include shortcodes and or JS code

Signed-off-by: Zhou Fang zhou.fang@eclipse-foundation.org

Before the changes, .Summary will take any content inside body->main (including shortcodes and or JavaScript code if exists)

So, replaced it with .Page.Params.summary to make sure it will only take the value set for the summary parameter in md file.

And added .Site.Params.description to have one more fallback choice for description.