W' expenditure and reconstitution calculator

Calculates the W' expenditure and reconstition during a ride.
The implementation is sub-optimal and will need to be optimised
and probably re-written to improve performance before v3.1 is
released.

This is based upon research conducted at the University of Exeter
by Philip Skiba, Weerapong Chidnok, Anni Vanhatalo, and Andrew Jones
and is used with permission.

For more information on the research please see: ""Modeling the
Expenditure and Reconstitution of Work Capacity above Critical
Power." Med Sci Sports Exerc 2012;:1.