Option tags supports quotation-mark-less values

Existing jBBCode cannot handle tags e.g.:

[quote=foo]bar[/quote]

These changes allow exactly that, while still allowing for other considerations (e.g. keyed option values).

I do recognise that there's a preg_match() used for a lookup ahead to peek for existence of a key value; alternative leaner/cleaner/etc solutions will be welcome.