Page specific and site wide assets

- [x] crawl and compile page styles https://github.com/adamrenklint/asimov/issues/4
- [x] crawl and compile page scripts https://github.com/adamrenklint/asimov/issues/5
- [x] crawl and compile site styles https://github.com/adamrenklint/asimov/issues/30
- [x] crawl and compile site scripts https://github.com/adamrenklint/asimov/issues/29
- [x] proper specs for compiled and written styles
- [x] proper specs for compiled and written scripts