VulkanSceneGraph-1.0.3 release

Major changes in this release are:

• Building of glslang source code directly into the VulkanSceneGraph library, avoiding the need to link against glslang and SPIRV-Tools as external libraries. Now the only dependency is Vulkan, C++17 and CMake and ensures that all platforms have the same shader compilation features available at all times.
• Instanced billboards with scaling support, all managed in the vertex shader with no CPU overhead.
• Rendering whole earth Bing Maps paged imagery.
• Support for aliasing extensions when loading data.
• New .txt Reader for reading ascii files as vsg::stringValue making it easier to read configuration files etc. in a coherent way that fully supports use with http and local file caching.
• Improvements to Windows and macOS keyboard mappings that ensure the same mappings are used on all platforms.
• Improved handling of two sided lighting.