Turn the app into rails engine

[runlevel5]

IMHO there are many distinct advantages to make enki Rails engine:

• Replace RAILS_RELATIVE_URL_ROOT with route mount path
• Mount enki on top of existing app for blogging features
• Distribute as Gem instead of source

[xaviershay]

As long as it is easily comprehendible as a stand-alone app. I don't want to have to understand anything about engines to be able to use enki.

[runlevel5]

@xaviershay in fact users need to have a basic understanding of rails engine if they want to extend or tweak. spree project's done this for a while and not many people seems to have problem with extending it.