Improve dashing config

[okletzmayr]

I was super happy to find a ready-made Dashing config in this repo. :) After using it for a while I worked on some improvements:

1. Class members and methods are now detected and can be searched for more easily.
2. Some files are not indexed (such as global.html) as they were producing duplicates in the search index.
3. Specify the root directory when running via npm run build-docset. This reduces the docset size by quite a lot, especially when the user generated the out/ folder for themselves (380MB -> 120MB in my case).