delete_collection now accepts a list of collections to delete.

Conflicts:
	pyzotero/zotero.py
Revert "delete_collection now accepts a list of collections to delete."

This reverts commit 637025b2702084d34110a2bc4320e04e9e3f3e1f.

It was done in the wrong branch.
delete_collection now accepts a list of collections to delete.

Conflicts:
	pyzotero/zotero.py
Merge branch 'delete_multiple_collections' into dev
Fix delete_collection headers for Py3
Updating delete_collection docs