sabre/dav 3.1 released

We're a bit late to the party, but we finally have a PHP 7 compatible release for sabre/dav.

The master branch had PHP 7 support for a while. The original plan for 3.1 was to include CalDAV sharing support, but this has been taking longer than expected.

The result was that we have not had a stable PHP 7-compatible release. So instead of waiting until all the 3.1 features were ready, we've figured it's better to get 3.1 out as soon as possible and move the new features over to a future 3.2 release. So here it is, 6 months after the last major release!

Aside from PHP 7 support, there's a few other changes:

• The minimum PHP version is now PHP 5.5.
• We switched to vobject 4
• We have support for "Calendar availability" in CalDAV. This feature allows users to specify what their work hours are (using compatible clients). This information will then be taken into consideration when generating freebusy responses.
• Lots of memory improvements, stability fixes and better exception messaging.

Contrary to past 'major' releases, this should be fairly easy for people to upgrade to. The BC changes will only affect a very small group.

• For a full list of changes and BC breaks, read the migration document.
• Check out the Changelog if you need even more detail.
• Use composer, or download the zip to get started with this.

This release also marks the beginning of the 'life support' period for sabre/dav 3.0.x. We'll continue to do bugfixes for another 12 months.

Happy new year!