build: Add support for CMake builds

[gulfemsavrun]

1. Add a root CMakeLists.txt file to provide cross-platform build support, making it easier to link against OpenCSD in large external projects.

2. Generate native CMake package files using OpenCSDConfig.cmake.in template.

[mikel-armbb]

Hi,
I've tried out the cmake patch you provided on linux initially. It works in as far as it goes. However the lack of building the .so files etc for linux is an issue - any build update needs to be comprehensive and produce the same output per platform as the original build process.

The cmake install method installs far more header files than the linux install - at present the linux install only adds sufficient for using the c-api based library. There is also no uninstall option within the cmake solution

In short, what you have provided may be sufficient for build into a larger project - adding cmake to the library should also allow a standalone build that produces the same results as the existing build.

Regards

Mike