agenda+ Changes to vertical text article

https://w3c.github.io/i18n-drafts/articles/vertical-text/index.en.html

This update:

- rewrites the section "The sideways value of text-orientation" 
https://w3c.github.io/i18n-drafts/articles/vertical-text/index.en.html#other-orientation
- updates many of the results to reflect progress in browser implementations
- brings all the 'try it yourself' pages into the document itself and 
applies the latest template and approaches
- various other edits

Please take a read and let me know by Thursday, if possible, whether 
anything needs to be changed before republishing.

ri