First pass at refactoring filter execution

This is the beginning of addressing #523.
Filtering optimisations
Optimise link widget

Handle the classes better, and stop using a default tooltip (parsing
the tooltip was a performance hog)
Optimise ordering of filter expressions

We get a significant speed improvement of >10% by rearranging filter
operators to bring to the front the operators likely to reduce the size
working list.
Add a sourceURL to the end of eval'd code

This, miraculously, lets Chrome dev tools list tiddler modules in the
script tag by their proper titles. Which lets you set breakpoints
within them!!!!!

https://chromedevtools.googlecode.com/svn-history/r421/trunk/tutorials/b
reapoints/index.html#regular
Fix problems with tiddlers called `__proto__`

Background:

http://www.2ality.com/2012/01/objects-as-maps.html
Fix problem with fields called "__proto__"
Ensure fieldnames are not wikified

`__proto__` was being wikified into underlined text
Fix problem with search filter operator
Update link widget docs
First pass at a release note for 5.0.9
Merge branch 'saner-filters'