added support for web-mode, jade-mode and stylus-mode (derived sws-mode)

`web-mode` provides multiple languages/styles per buffer, but the main (and common in this mode) is `html`. Also, there are multiple vars focused on the indentation offset per language (by default all have the same value, and all are loaded under this mode).

I think it is not supported different highlights (offsets) per buffer with this mode. So, I think this is the best option nowadays.