This adds a public header so that applications can get the Wayland
version number at compile time. This can be used to make applications
that support compiling against multiple versions of Wayland.

There is a separate installed header called cogl-version.h which gets
included by both wayland-client.h and wayland-server.h

The canonical place for the version number is the configure.ac script
which splits it into three separate m4 defines for the major, minor
and micro version. These are copied into the generated
wayland-version.h header using AC_SUBST. There is also a string form
of the complete version number.

The version number is now also automatically copied into the two .pc
files.

Because the major, minor and micro parts are required it is no longer
possible to leave the version number as 'master' when building from
git. Most projects seem to immediately bump the git repo to a fake
version number (usually odd) after making a release so that there is
always a relative number that can be used for comparison. This patch
sets the git version to 0.99.0 under the assumption that the next
release will be 1.0.0.