New: Text formatting via macros

I (ChrisSiebenmann) found myself with a genuine need for text set in HTML <strike>. Rather than try to invent a formatting setup for this that did not make me cringe, I just punted to the easy solution: macros that do text formatting.

So, DWiki now has grown the new macros:

• ST for the font styles DWiki didn't already have.
• C for character entities, and ShowCharEnts to show the named entities we support.
• because I was there anyways, AB for <abbr>, so I could have those cute inline abbreviation expansion things. Tragically <abbr> is not supported by IE 6 and less, so AB may quietly change to generating <acronym> someday.
• and finally, IMG to generate <img>. Width, height, and alt text is mandatory, and there is a hacky way to also roll title text in too. (Title text is optional.)

Through special black magic, ST, C, and AB can be used in comments (the omission of IMG is deliberate). In theory this lets a commenter cause character set explosions, but in practice a bad commenter can just write UTF-8 directly (UTF-8 is the common and only sane character set choice, so).

Implementing these as macros means that they have some limitations. You can't nest C, AB, or a differently styled ST inside an ST, and currently none of them can be done inside link text ([[....]]).

These macros are a bit of a hack. It's relatively easy to implement bits of HTML this way, but I'm not sure if it's good design overall.