Attachments template plus fluid images and objects

This branch adds content templates for general attachments as well as a specific template for images. Additions to the stylesheets also ensure that images and embeds don't exceed the width of their container, and should ensure the height of images also auto-adjusts where the width is scaled down to maintain the proper aspect ratio.

The version has been bumped to 0.2.0-alpha, and additional branches can continue to develop toward the 0.2.0 milestone.