Define term for "symbol" form of "and" (ampersand)

[rmzelle]

See https://forums.zotero.org/discussion/32447/ . Some locales (such as Chinese and Slovenian) use a symbol different from an ampersand, so it's desirable to be able to (re)define this term.

As discussed in that thread, there are three issues:

• Defining this term form in the locale files is rather trivial, but to avoid problems it would probably be good to put this change in a 1.0.2 release. That way we can make sure all distributed 1.0.2 locale files have the term.
• CSL processors currently hardcode this delimiter (since it's absent from the CSL 1.0.1 locale files), and we have to make sure they recognize this term. (another reason to make this a 1.0.2 change)
• Some locales don't use spaces around the symbol, or only on one side. As proposed by @fbennett, we could handle the latter case with an explicitly defined space.