Extend Feed to support CSS style sheet specification

[meyercr]

Hello Suin,
Thank you for your useful library.
Are you interested in supporting CSS Style sheets for RSS feeds? This change adds support for including a Style sheet in the XML.

$feed->addStyle("", "<optional media specification - defaults to screen>")

Thank you,
Craig

[suin]

@meyercr Thank you for PR😆 CSS style sheets for RSS sounds interesting! I would like to merge your great work. Could you brush up your cool changes?

1. Could you remove debug code for production?
2. Could you follow camel case naming for style consistency? For example, feedStyles would be much consistent than feed_styles.

Thank you

[meyercr]

Thank you for your interest.
I have removed the debug() code, I had forgotten in was there.
And I have used camelCase as you suggested.
I have pushed the differences up to GitHub, do I did to resubmit the Pull Request?

[peter279k]

Is anyone concern this PR?
This PR is great and it's need to be reviewed and merged 👍 .

[jaspal747]

Suin.. do you mind merging this?
Thanks