Added class name setting to inline style syntax

* You can now, in addition to setting styles using the @@ inline style
syntax, also set a class name for the generated <span>, thus making it a
shorthand for <span class="..."></span>. Writing @@.name;...@@ will set
the class of the span to "name". Writing @@.truth.electronic.big;...@@
will give it the "truth", "electronic" and "big" classes. This can also
be mixed with regular styles. This was inspired by TiddlyWiki5's
variation of the TiddlyWiki inline style syntax.
* Altered History.prototype.saveVariables so that the setter link code
is simpler. This fixes a bug where variables in setter links were being
passed by reference rather than value.