Improve .htmlhintrc handling

[bezoerb]

currently the .htmlhintrc needs to be specified relative to the project root.

Maybe something like this would be much nicer:

• Try to autodetect file based on the current filepath up to the project root
• When file is found -> use (no explicit htmlhintrc setting needed)
• When file is specified, use specified one
• Specified rules will overwrite rules in .htmlhintrc

[ghost]

I think it should follow what eslint does.

eslint has a root rc, then sub rc files can override the root or compliment it. A top-down approach.