* CMake: Prefix options with "YAML" and hide platform-specific options
When including yaml-cpp as a subproject, some option names can conflict with other projects.
(1) Make sure the yaml-cpp options are prefixed with YAML
(2) Hide platform-specific options when possible to avoid cluttering the cmake option list
* Update docs for change from BUILD_SHARED_LIBS to YAML_BUILD_SHARED_LIBS
Setting CMAKE_CXX_STANDARD and CMAKE_CXX_STANDARD_REQUIRED directly is problematic when including yaml-cpp as a subproject.
The proper way is to set these per-target.
Andy MaloneyandJesse Beder
