Merge branch 'build_cmake' of https://github.com/TcT2k/wxWidgets

Add CMake-based build system.

Merge the original branch without any changes except for resolving the
conflict due to moving the contents of .travis.yml to a separate file by
propagating the changes done in this file since then to the new script
and rerunning ./build/update-setup-h and ./build/cmake/update_files.py
to update the file lists changed in the meanwhile.

Closes https://github.com/wxWidgets/wxWidgets/pull/330

appveyor.yml

@@ -32,6 +32,10 @@ environment:
   - TOOLSET: msys2
     MSYSTEM: MINGW32
   - TOOLSET: cygwin
+  - TOOLSET: cmake
+    GENERATOR: 'Visual Studio 12'
+    SHARED: ON
+    CONFIGURATION: Release
 
 clone_depth: 50