add --include flag

builds off #30 (since i couldnt run specs otherwise), so until that's merged, [this diff](https://github.com/afeld/rawler/compare/1.9-fixes...include) is more accurate.  this PR this adds a --include flag  (and --iinclude, which i don't love but wanted to be consistent), which is like the opposite of --skip: it will only crawl subsequent pages that match the provided regex.

also [randomized the spec order](https://www.relishapp.com/rspec/rspec-core/v/2-14/docs/command-line/order-new-in-rspec-core-2-8) to find the places that the module wasn't being reset, though i think it's good to keep that option enabled anyway.