REM length unit is missing in MACROS

[alexrichterxyz]

The CSS "rem" unit is missing here

cssutils/cssutils/profiles.py

Line 91 in 57179fe

'length': r'0|{num}(em|ex|px|in|cm|mm|pt|pc)',

[jaraco]

At first blush, it sounds like an easy fix. Would you be willing to explore it and add support for it and add it to the tests if relevant (if there's already tests for each length unit)?

[rdcrampton]

I've submitted a PR (#69) for this. In addition to rem, I also added ch, vh, vw, vmin, and vmax since those CSS3 viewport and relative units were missing from the same regex. Let me know if you'd prefer I keep it scoped to just rem.