Added url pattern, view, associated settings, and robots.txt template (not a static file).  Fixes #143.
Merge branch 'master' into t143_robots
Removed unnecessary support for sitemap indexing.
Merge branch 'master' into t143_robots
Resolved merge conflict
Used django.views.generic.TemplateView to further simplify serving robots.txt
Removed commented line
Merge pull request #155 from gwu-libraries/t143_robots

Fixes #143