rabbitmq-c v0.12.0

Changed

• rabbitmq-c now compiles as C99
• CMake 3.12 is new minimum required version
• CMake -DBUILD_TESTS renamed to -DBUILD_TESTING
• CMake -DBUILD_EXAMPLES now defaults to OFF
• CMake -DBUILD_TOOLS now defaults to OFF
• Unix library version now matches the release version, SONAME remains the same.
• Modernized CMake scripts to better adopt modern standards
• Public headers have moved to rabbitmq-c/ directory
• Dropped support for MSVC older than VS 2010
• Dropped support for OpenSSL v1.1.0 and older
• Minimum SSL version set to TLSv1.2
• Updated to RabbitMQ framing to v3.8.19