Allow for flat indexing

[senorsnrub]

This is similar to the default view that tumblr gives. Also has paging & tags support

[bbolli]

Thanks! One remark, though: It looks like you copied a lot of code from class Index. Can you make class FlatIndex a subclass of Index to reduce the duplications?

[senorsnrub]

Yeah I can clean it up a bit. It actually doesn't share very much actual logic - I think just the initializer, where some of the variables aren't being used. I think not having them subclassed makes more sense(or creating an abstract superclass that exposes the interface - basically just add_post and save_index) . Thoughts?

[tari3x]

+1 to this, would love to see it merged!