Easier calculation variations

[cbailiss]

pivottabler supports variations of calculations such as % of row total, etc as described here:
http://www.pivottabler.org.uk/articles/vA2-appendix.html

These calculations are however cumbersome to use in a pivot table (having to explicitly work with filter overrides).
Design a set of easier to use wrappers.
Look at common calculation variations in use elsewhere (e.g. the various "display as" options for a calculation in a pivot table in Excel).