Moved Driver.populate_state out of init

Moved Driver.populate_state() out of __init__(). Since we want to scrape the
first page also when we do our crawl, it doesn't really belong there,
since it fetches the first page. Also, it seems odd to have something
that does an http request inside the constructor of a class.
Added a sample script and updated README

Sample script initializes a Driver and sets off the crawl process. The
crawler doesn't have any output mechanism hooked in yet, so there's no
visible output at all.