Some minor doc fixes, and a fix to ensure that all links are properly rewritten to include the site base URL.

Also, a reverse from the last release that added an annoying background color to the footer of the default theme (and, by extention, any theme extended from the default theme).

Full changelog below...

• add command docs to Blog app
• show how to create plain page in content guide (#336)
• clarify some parts of the content guide (#335)
• fix "/" not being rewritten with base URL (#337)
• add module list to Statocles::Help (#322)
• move test::lib to test to fix xt/ tests
• remove background and border from default footer