Added MapArt Systems

A new startup from the guys at SecondSite, LLC. More at http://mapartsystems.com/ (navigate with arrows or controls in bottom-right).
Edited index.html to add new entry, added image at img/startups/mapart.png
We're glad y'all are doing this. Thanks for letting us be a part.
  -Reed Tomlinson
   reed@secondsitellc.com