Added parameter() for shorthand <<display>> calls

You can now supply additional arguments to the shorthand <<display>>
macro - in effect, you can "call" passages as if they were macros. (This
is inspired by the "widget" functionality present in Thomas M. Edwards's
SugarCube format.) The parameter() function returns one of the
space-separated terms in the macro invocation, parsed to a value. The
function's argument is a zero-based index - parameter(0) returns the
first parameter, parameter(1) the second, and so forth.

Previously I'd considered a specific "widget" passage type that would
solely permit this type of shorthand call. However, with the advent of
shorthand <<display>> syntax, the necessary distinction between
"widgets" and ordinary passages is now almost absent.
Added CSS syntax highlighting

Only the basic wxPython CSS highlighter is being used. It recognises
most CSS syntax structures, but isn't all that helpful about
highlighting errors or omissions.

Also fixed some Twine passage syntax highlighter bugs.
Added CSS-based transitions

The old fade() method, while functional, is nonetheless not that
customisable. This lays some groundwork for transition customisation by
making them entirely CSS-based, with their CSS being in a separate
<style> element. (IE8 will fallback to fade() naturally.)

Also fixed some IE8 bugs.
Added utilities for scripts

* setTransitionCSS() replaces the contents of the #transitionCSS
<script> element with the passed string. This allows you to completely
override the default transition CSS without it cascading down. I'm
offering this as a JS function because many transitions will also
require some extra JS, and being able to provide the complete transition
code in just a script is desirable.
* prerender and postrender are objects whose function properties are
executed every time the passage is rendered. The functions added to them
take one argument: the resultant .passage .content element. Their 'this'
value is the Passage object being rendered.
* Changed Jonah's .body element's class to .content, to match Sugarcane.
* Fixed a bug in Wikifier.prototype.fullArgs().
Some transition CSS tweaks

* Made setTransitionCSS work with the [img] syntax.
* A passage tagged with "stylesheet transition" will have its contents
replace the #transitionCSS <script> element. A similar passage tagged
with an extra tag after that will only apply that transition to passages
with a matching tag. So, you can now apply pure-CSS transitions to
specific tags.
Jonah and <<choice>> changes

* Clicking a link in a past passage in Jonah now rewinds the game state
to that passage before following the link. This gives the author a
greater level of control over the game state - it's no longer possible
to re-use old links from earlier in the story that no longer make sense
in the current context. And, the act of using older links is now more
like "exploring story branches", in that the current branch of the story
is forgotten in favour of the new link's branch. All in all, I believe
it's a good change.
* <<choice>> is now a proper macro in Sugarcane. Instead of merely
creating a link, it now creates a link that can only be clicked once. In
that respect, it now functions like a more atomic <<actions>> macro.
No "|" symbols in passage titles.

The pipe "|" is no longer permitted in passage titles.

Also, text drag-and-drop passage creation now abides by previous passage
title constraints.
Improved <<choice>> arguments

<<choice>> can now accept arguments phrased using the link syntax, e.g:
<<choice [[a trapdoor?|falling]]>>. This saves the trouble of having to
account for its inconsistent argument order.
Fixed bug in IDE's <<choice>> link parsing

Links in <<choice>> instances should now be correctly parsed by the IDE.
<<back>> now usable in Jonah

When used in Jonah, a <<back>> link removes the contained passage, plus
any prior passages (as given by the "steps" argument or a passage name
argument).

Also fixed some tiny <<back>> bugs, and gave Jonah some CSS that dims
past passages.
Fixed Jonah scrolling in IE 8
Added "Undo" StorySettings option

This option provides the author with control over how Sugarcane and
Jonah handle past passages. If it's off, Sugarcane won't allow use of
the browser back button, and Jonah will disable links in all but the
bottommost passage div.
Merge pull request #89 from webbedspace/master

Further additions