Add a Bower definition for distribution

[anthonny]

See asciidoctor/asciidoctor.js#46 (comment)

The target is to provide all the other themes in a Bower repo.

Btw, we'll get to play with some new tools here because we need...for our sanity...some visual QA for the stylesheets.
@mojavelinux

[mojavelinux]

I added a related issue for the visual QA: #16

[mojavelinux]

I think we can also provide the default theme here as well.

We'll want two publish at least two versions of each theme...one for a use with a full HTML document and one for use when you are using the embeddable HTML. I had started a branch with this split, but I haven't merged it in and now it needs some updating.

https://github.com/asciidoctor/asciidoctor-stylesheet-factory/tree/embedded-stylesheets

[mojavelinux]

Note that we're tracking the refactoring to create stylesheets for embeddable HTML in #18.