Change @:useParentTemplate to @:skipTemplating, change @:dtxdebug to @:dtxDebug
Moved KeepWidget to separate file

Having it as a submodule of Widget was causing me issues in the macros
Use Context.fatalError rather than Context.error to make things easier to diagnose
Better handling of type failures in detox loops.

Before it was incorrectly catching all sorts of errors and hiding them
behind "can't type dtx loop".  Which made debugging near impossible...

Fixed now :)
Make loop partials use KeepWidget, and support keep="true" attribute on other partials.
Removed comment that was no longer relevant
Update tests for KeepWidget changes
Option to cache widgets.  Should result in faster parsing
Simple temporary test to compare speeds of widgets
Bump version