Configuration and compile documentation improvements.

* Improve the stable and testing build version option logic.
* Use CMake FindPythonInterp to configure the Python interpreter.
* Use Python interpreter to determine the system Python module install
  path if not already defined on the command line.
* Add header symbol checks for asinh(), acosh(), and atanh().
* Add test source to check for isinf() which can be defined as a C++template.
* Replace conditional compile on windows systems for aXXXh() with CMake
  configuration tests.
* A few minor MSVC compile fixes.
* Fix incorrect python environment string in fixswigimports.py
* Create a separate document for KiCad CMake build options.
* Create a separate how to compile KiCad on Windows document.

common/class_plotter.cpp

@@ -387,7 +387,8 @@ void PLOTTER::segmentAsOval( const wxPoint& start, const wxPoint& end, int width
     else if( size.x == 0 )
         orient = 900;
     else
-        orient = -(int) ( RAD2DEG( atan2( size.y, size.x ) ) * 10.0 );
+        orient = -(int) ( RAD2DEG( atan2( (double)size.y, (double)size.x ) ) * 10.0 );
+
     size.x = (int) sqrt( ( (double) size.x * size.x )
                        + ( (double) size.y * size.y ) ) + width;
     size.y = width;