Add support to "fit-content" on width property

**Is your feature request related to a problem? Please describe.**
I've been trying to generate a PDF with chat messages and I kinda want to emulate the style for each text bubble but the problem is: even smaller messages will have its background occupying 100% of the available space.

The library doesn't support the property `fit-content` so it's been really annoying.

**Describe the solution you'd like**
Allow the `width` property to receive a value `fit-content` to indeed fit its content size.

**Describe alternatives you've considered**
There's none.

**Additional context**
None.