This adds documentation for the `templateResult` and
`templateSelection` options. The fact that placeholders and
custom messages are templated was noted, although most people
should be using the standard `text` property that they provide
anyway. This fixes the templating link provided in the release
announcement to link to the correct location in the documentation.
This also adds support for the `templateSelection` function to
return a DocumentFragment or jQuery compatible object to be
passed back and rendered.
This closes https://github.com/select2/select2/issues/3005.
This closes https://github.com/select2/select2/issues/3019.