ADD: new track message, Entity class and Position class

libs/geographiclib/wrapper/octave/README.md

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+# Calling GeographicLib C++ library from Octave/MATLAB
+
+The Octave/MATLAB package
+[geographiclib](https://github.com/geographiclib/geographiclib-octave#readme)
+provides a native Octave/MATLAB implementation of a subset of
+GeographicLib.  This is also available via the MATLAB Central Package
+[geographiclib](https://www.mathworks.com/matlabcentral/fileexchange/50605)
+
+It is also possible to call the C++ GeographicLib library directly
+from Octave and MATLAB.  This gives you access to the full range of
+GeographicLib's capabilities.
+
+In order to make use of this facility, it is necessary to write some
+interface code.  The files in this directory provide a sample of such
+interface code.  This example solves the inverse geodesic problem for
+ellipsoids with arbitrary flattening.  (The code `geoddistance.m` does
+this as native Matlab code; but it is limited to ellipsoids with a
+smaller flattening.)
+
+For full details on how to write the interface code, see
+
+  https://www.mathworks.com/help/matlab/write-cc-mex-files.html
+
+To compile the interface code, start Octave or MATLAB and run, e.g.,
+```Octave
+mex -setup C++
+help geographiclibinterface
+geographiclibinterface
+help geodesicinverse
+geodesicinverse([40.6, -73.8, 51.6, -0.5])
+ans =
+
+   5.1199e+01   1.0782e+02   5.5518e+06
+```
+
+The first command allows you to select the compiler to use (which should
+be the same as that used to compile GeographicLib).
+
+These routines just offer a simple interface to the corresponding C++
+class. Use the help function to get documentation,
+```Octave
+help geodesicinverse
+```
+
+Unfortunately, the help function does not work for compiled functions in
+Octave; in this case, just list the .m file, e.g.,
+```Octave
+type geodesicinverse.m
+```