Added new section to Documentation - "Guides and How-tos"

As in issue #220 - Created section with necessary menu additions and new base page. Further additions to Guides and Howtos can be made in the new directory. Simple guides can be placed there instead of in the CCK.

@natmey @critzo @sifrwahid @dismantl @jheretic - Please review and comment on this section. If there are no questions or concerns, please merge!