Allow use of calculated fields in roll templates

ShadowRun (and other games) really requires the use of calculated fields in roll templates, both as part of the roll and just for display purposes. This means full access to ceiling, floor, and round functions in any template section and both before and after the "d" in a die roll. This includes being able to use these formulas in inline rolls using [[ and ]]. Right now, certain rolls which work just fine when sent as /r don't work at all when sent inline for use in a template.

This is needed in the Ghostbusters sheet that OldSchoolChris and I have been working on. There's a need to show a "Ghost Die" and also have that die summed with some others in the dice pool.