Promote applicable 'caniuse.com' feature requests

[tgraham-antenna]

'caniuse.com' is possibly the most popular website for checking what is and isn't supported in browsers.

Its list of feature requests is at https://caniuse.com/issue-list.

The issues list is generated from GitHub issues: https://github.com/Fyrd/caniuse/issues

For example, the request for an XSLT support table (currently 17th in the list) is at Fyrd/caniuse#1722.

To organise people to do a flashmob of +1s on particular feature requests would be anti-social. However, it might do to point out the XML-related feature requests and let people add their +1 to whichever issues interest them.