Create a CMake Config.cmake, etc.
Fix bugs with cmake config files.
Fix Config file lepton include path.
[cmake] Need newer CMake for ConfigVersion macro.
Fix lib path for windows.
[cmake] Use different macro for ConfigVersion.
[cmake] Remove accidental inclusion of ApiDoxygen.
[cmake] Update sample CMakeLists.txt.
Plugins now use the new OpenSimConfig.cmake.

Also the plugins weren't compiling. Fixed the errors and loosely checked
that the results were close to the expected results.
Merge pull request #187 from chrisdembia/cmake-config-files-2

Provide OpenSimConfig.cmake file