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This adds yaml-cpp-config.cmake, yaml-cpp-config-version.cmake, and
yaml-cpp-targets.cmake to the cmake install. As a result, cmake's
find_package can easily find yaml-cpp for software that depends on
yaml-cpp.

Add code to install cmake files to $CMAKE_INSTALL_PREFIX/CMake on
Windows, which is the de-facto standard.

Closes jbeder/yaml-cpp#336 jbeder/yaml-cpp#127

 - Adds 'std=c++11' compiler flags
 - Replaces boost::type_traits with std::type_traits
 - Replaces boost::shared_ptr with std::shared_ptr
 - Replaces std::auto_ptr with std::unique_ptr
 - Replaces raw pointers with std::unique_ptr in ptr_vector, ptr_stack, and SettingChanges
 - Replaces boost::noncopyable with deleted copy and assignment operators
 - Replaces boost::next with std::next
 - Replaces boost::enable_if with std::enable_if
 - Replaces boost::is_convertible with std::is_convertible
 - Replaces ptrdiff_t with std::ptrdiff_t
 - Replaces boost::iterator_facade and boost::iterator_adaptor with std::iterator, borrowing the 'proxy reference' technique from boost
 - Removes Boost dependency from CMakeLists
 - Formats changed files using clang-format

- ensures shared library code is position-independent.

Add yaml-cpp-config.cmake and yaml-cpp-config-version.cmake files for importing yaml-cpp into external projects (through find_package).

Fix clang compiler settings, and properly set up warnings so they don't interfere with gtest and gmock

Split the yaml.h file into new/old API, which we'll then copy to yaml.h at build time (so the right one gets installed)

Set the default build to the old API, and removed the duplicate spec test implementation for the old api

Major switch from Value -> Node. The library compiles with the new API, but tests are still oldies, and don't compile

Refactored parse.cpp so that VS doesn't complain, added MinSizeRel build setting, and fixed numbering in the spec tests