Add function getdim for easy dimensionalizing of coefficients

[cibinjoseph]

This PR adds the bookkeeping function getdim() that computes dimensional thrust, torque and power from their coefficient forms. The function takes similar inputs as the existing nondim() function. Documentation and unit tests for the function are also included.

Utility:

1. The rotor object exposed by the CCBlade package is of a general nature. This function may find use in other codes that output aerodynamic forces in non-dimensional coefficient forms.
2. Scenarios like rotor trim may require input in thrust or torque coefficient form and transforming to dimensional form.