limit rss feed for some services that have limits (like feedburner)

Conflicts:
	app/controllers/refinery/blog/posts_controller.rb
add max_results feature to readme

Conflicts:
	readme.md
Move down "Additional Features" section in readme.

This also adds "More Information" section.

Conflicts:
	readme.md
Need to call html_safe on unsafe string before concatenating it to safe string.

Read explanation at
https://github.com/refinery/refinerycms-blog/issues/325#issuecomment-198
07945.

Closes #325.

Conflicts:
	app/views/refinery/blog/posts/_nav.html.erb
Add reCaptcha for blog comments.