Public domain does not have an internationally agreed upon definition,
As such it's generally preferred to use an extremely liberal license,
which can explicitly list the rights granted by the copyright holder.
The CC0 license is the usual choice here.
This "relicensing" is done without hunting down copyright holders, since
it is presumed that their release of this work into the public domain
authorizes us to redistribute this code under any other license of our
choosing.
Ideally Common.h wouldn't be a header in the Common library, and instead be renamed to something else, like PlatformCompatibility.h or something, but even then, there's still some things in the header that don't really fall under that label
This moves the version strings out to their own version header that doesn't dump a bunch of other unrelated things into scope, like what Common.h was doing.
This also places them into the Common namespace, as opposed to letting them sit in the global namespace.
