This tries to uniform the naming convention to US notation.

This ensures the tests are still passing with the new definition of
Polars (i.e. change from structure to object).

It also removes many duplicate tests (error tests based on inputs).
These tests are now only done on the parser functions and not the main
caller function. This simplifies test updates and reduces testing time.

Use Polar object instead of using a loosly defined Polar structure.
This adds robustness to these functions and will simplify future
developments.

BREAKING CHANGE: xf2mat no longer generates structures.
BREAKING CHANGE: any function that could took a polar structre as
input must now take a polar Object instead.

Keep Readme short and readble. The doc should be fully contained in the
MATLAB code of each function/class.

This commit also adds details on how to use classes and the description
of the Polar class.

The previous way of doing stuff was not allowing to load files from
multiple (sub)directories. This commits allows the user to specify
files from various directories as a string array.

BREAKING: This commit changes the input arguments for **xf2mat** and
**formatairfoilcoord**.

The two functions now return one single matrix with both coordinates
instead of separate vectors.

Nacaairfoil can also return the data in either Selig or Lednicer
formats.

This expand the scope of the function to convert any entry format into
an other output format.

Signed-off-by: Thomas Lambert <t.lambert@uliege.be>