[WIP] Bolean attributes serialization

Added a way to decide what attributes are `boolean`
Here I'm saying which are the attributes that are not boolean. So, any empty attribute by-default is boolean.

With this configuration you can just avoid to have this `<img src="xxxx" alt>`,  which is not correct.

If the `autoplay` attribute is set to ` ` (empty value) it will be outputed as `<video autoplay>`
otherwise will be  `<video autoplay="something">`