API changes! This must match the versions of ding_availability, ding_periodical.

- Let ding_availability decide what character to put between the holding parts. So return an array of holding parts instead of a string.
- Provide holdings info for periodicals
API change: However, it is backwards compatible, so it works with older versions of ding_availability.

Support the new $only_available option for holdings.
Merge branch 'refactor' into merge

Conflicts:
	includes/alma.availability.inc