Generate zotero://select/ link for all Zotero items

[rmzelle]

Zotero recently added the ability to select multiple Zotero items in a user's library via a zotero://select/ link with item keys, using the syntax:

zotero://select/library/items?itemKey=ABCD2345,BCDE9876

Generating this link from extracted metadata would be useful for users who still have access to their original library. Running their manuscript through ref-extractor and using the zotero://select/ link probably would be the easiest way to identify which items have been cited, at least until Zotero introduces proper document collections (zotero/zotero#21).

(see also https://forums.zotero.org/discussion/75794/feature-request-allow-multiple-item-selection-with-zotero-select)