The Clutter backend split is opaque enough that should allow us to just
build all possible backends inside the same shared object, and select
the wanted backend at initialization time.
This requires some work in the build system, as well as the
initialization code, to remove duplicate functions that might cause
conflicts at build and link time. We also need to defer all the checks
of the internal state of the platform-specific API to run-time type
checks.
Make Cally follow the single-include header file policy of Clutter and
Cogl; this means making cally.h the single include header, and requires
a new cally-main.h file for the functions defined by cally.h.
Also:
• clean up the licensing notice and remove the FSF address;
• document the object structures (instance and class);
• G_GNUC_CONST-ify the get_type() functions;
• reduce the padding for CallyActor sub-classes;
• reduce the amount of headers included.
