Two 4-Digit Airfoil Classes

[ddmarshall]

There should be two separate classes for the 4-digit thicknesses:

• [x] One that uses the standard coefficients and can only take parameters that are canonical parameters matching the 4-digit spec.
• [x] One that solves for the thickness coefficients and can produce sharp trailing edges, use radius spec. instead of the 0.1 chord thickness, and can take floating point values for all three parameters associated with the 4-digit airfoil.

Note that these two will not produce the exact same airfoil when provided the same settings because of the errors in the standard coefficients.

[ddmarshall]

Commit f1fa3293 addresses this issue.