Make capitalization of DogStatsD consistent

(Includes some other cosmetic fixes too)
Link mentions of IRC to Freenode's web client
Minor content edits (e.g. typos)
Improving design fit and finish on docs site

 - Moved CSS to sitewide stylesheet
 - Added corpweb-inspired header and buttons
 - Moved page title into content area (for now)
 - Made the sidebar navigation affix
Revise titles for guides
Substitute larger logo in nav
Correcting Nitpicks

 - Renamed sidebar link that wrapped
 - Moved Overview link to Guides
 - Added terrible pun
 - Fixed padding/border on code listing tabs
 - Put footer in _footer.html, included everywhere
 - Use correct -fluid classes for API page
Merge pull request #80 from DataDog/polishing

Improved design and usability for the docs