Add the turbulent boundary layer experimental data.

Experimental data from Wieghardt and Tillmann (1951)
to be used in the notebook about the boundary layer correction.
The data have been found here: http://www.grc.nasa.gov/WWW/wind/valid/fpturb/fpturb.html.
Add a test case of the flat plate.

Add the flat plate example to test the BoundaryLayer class.
Comparison with experimental data and the Blasius solution.
Experimental data from Weighardt and Tillmann (1951).