Improved event bus to handle arbitrary events [CEL-54]
Removed core tests and fixed CMake build
Added platform configuration headers
Merge branch 'generic-events'
Merge branch 'bifrost'

Conflicts:
	src/tests/CMakeLists.txt
Renamed source files to *.cc instead of *.cpp
Updated CMake build files to use new source naming
Compile modularization of core engine components
Added mkdocs documentation
Added NativeExtensionLoaded, NativeExtensionsLoaded, PreExtensionLoad, PreSubsystemCreate, SubsystemCreated events
Added support for library reloads to ISharedLibraryLoader and SoLoader; also updated SoLoader tests accordingly
Added IExtensionSearcher interface and default implementation
Fixed consistency in *System* <-> *Subsystem* naming
Replaced GpuBufferManager with IGpuBufferManager in engine core