Add more stylesheet units for the length regex

[markusguenther]

Add px, pt, em, ex and pc as CSS units to detect the length. Otherwise a
pt value for instance can not be transformed.

I used the library without styled components and transform css for an htmlview. Then you can have other css units like points.

[jacobp100]

I’m not opposed to adding some of these, although currently 1pt == 1px (it should be about 1.333px).

I'm not 100% sure on adding units that depend on the current font size, since they won't work as expected—but we might be able to get away with rem.

[markusguenther]

I am nut sure if the library transforms pt to pixels. I got an error in my app because the pt was not transformed and react-native could not handle it. The other formats was just an addition.

[jacobp100]

You’ll need to get it to transform units to the pixel values. You can look at the CSS values spec for the conversions! In addition, if you wanted rem, you can do that based off a font size of 14px.

[markusguenther]

I adjusted my package now. So if this is not a general issue I close the PR.

Thanks for the fast feedback 👍