For bug reports it's very convenient to know the exact version. For
release builds, the standard version triplet (major.minor.micro) is
more than sufficient, but that's not the case for development builds.
Due to the post-release version increment, development builds already
have a version number that is distinct from previous releases, but
including the git commit SHA1 is even more accurate.
On Windows, the git commit SHA1 is also embedded in the version
resource.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.
