Fixed a shorthand <<display>> bug + other bugs

* Now, the shorthand macro tag's title won't sometimes be incorrectly
parsed as its first argument.
* Removed the "Delete Passage" menu item in the Story menu, due to an
identical entry being in the Edit menu.
* Added the data: protocol as a valid "external" link protocol.
* External links and variable links are no longer considered broken
links in the IDE.
* Engine: Added the passage() and tags() functions as aliases for
state.history[0].passage.title and state.history[0].passage.tags.