Add startPage option support for arbitrary initial page

Historically bookblock rendered the first page first. This adds support for
the client to specify what page to initially render.

This is useful for situations where it is desired to link directly to a slide
by using the hash of the URL.
Put config options in the readme
Revert "Put config options in the readme"

This reverts commit ecc866159863d2dc92ba65e3f70a81a531607fd5.
put configuration options in the *correct* README file
Merge pull request #17 from d3mcfadden/startpage-option

Add startPage option support for arbitrary initial page