[CSSWG][css-writing-modes] CSS Writing Modes: Updated L3, CR for L4

On 24 May 2018, the CSS WG published an updated Candidate Recommendation
of CSS Writing Modes Level 3 and an initial Candidate Recommendation of
CSS Writing Modes Level 4:

     https://www.w3.org/TR/css-writing-modes-3/
     https://www.w3.org/TR/css-writing-modes-4/

CSS Writing Modes defines CSS support for various international writing modes,
such as left-to-right (e.g. Latin or Indic), right-to-left (e.g. Hebrew or Arabic),
bidirectional (e.g. mixed Latin and Arabic) and vertical (e.g. Asian scripts).

This is a minor update to Level 3 to correctly handle 'max-height'
(in addition to 'height') when calculating auto sizes of orthogonal
flows:
   https://www.w3.org/TR/2018/CR-css-writing-modes-3-20180524/#changes-201712

Level 4 is the same as the Level 3 draft, except that it includes several
features that were dropped from the Level 3 CR due to lack of implementation:
   * 'sideways-lr' and 'sideways-rl' values of the 'writing-mode' property
   * 'digits' value of 'text-combine-upright'
   * multi-column handling of orthogonal block containers
This publication maintains its synchronization with Level 3 (and issues an
official CR transition; we had to wait a bit after FPWD to request the
transition).

Please review the drafts, and send any comments to this mailing list,
<www-style@w3.org>, prefixed with [css-writing-modes] (as I did on this
message) or (preferably) file them in the GitHub repository at
   https://github.com/w3c/csswg-drafts/issues

For the CSS WG,
~fantasai