Tidy up some source filenames:
* Add .unity suffix to mark unity sources
* Fix some relative include paths
Beast SCons tools:
* Add VSProject SCons Builder
* Add Protoc SCons Builder
* Add Beast build utilities python module
Improved SConstruct:
* Automatic source list built via directory iteration
* Build multiple toolchains and flavors simulaneously:
    - Toolchains: gcc, clang, msvc
    - Flavors: debug, release
* Documentation on aliases (top of the SConstruct file)
Fix rocksdb relative include