[Libosinfo] [PATCHv4] datamap support

[Christophe Fergeau]

Hey,

Here is another iteration of the datamap support patches. There are not
many big changes before patch 07/11. I took a different approach from the
previous series in that the values are only transformed when calling
the appropriate getter. This has the side effect of making the code
less complex, of making the implementation of the cloning function in
patch 10/11 easier, ... This also makes it easier to support modifications
of the OsinfoInstallConfig:config-params properties during the life
time of the OsinfoInstallConfig objects. And in turn, this makes
it easier to not force applications to use a new constructor, which would
be an ABI break.

Christophe