Check if it worth to save the feed as json (instead of XML)

[yadomi]

Currently:

• The feed is downloaded as XML
• the XML is parsed to js object
• the js object is stringified to JSON and saved to file

Then json file is then reparsed (via JSON.parse) when building the static page.

Maybe it could be less cpu consuming to save the XML as this and parse it using the xml module when building the feed.