API: fix versioning.

API: fix versioning.

We have to consider three distinct versions at this time: the VA-API
version, the library package version number, and the DSO version.

* VA-API version:
- increment major for any ABI change (which shall not occur!)
- increment minor for any interface change (e.g. new or modified function)
- increment micro for any other change (e.g. new flag, new codec definitions)
- reset micro version to zero when minor version is incremented
- reset minor version to zero when major version is incremented

* libva package version number:
- major version is automatically generated from VA-API major version
- minor version is automatically generated from VA-API minor version
- increment micro for any library release
- reset micro version to zero when VA-API major or minor version is incremented

* DSO version:
The SONAME shall remain to libva.so.1 for VA-API 0.x.y as long as the ABI
is not changed. Thus, the library name is generated as libva.<x>.<y>.0 where
<x> = VA-API major version + 1
<y> = 100 * VA-API minor version + VA-API micro version

For example:
VA-API 0.32.0 generates libva.so.1.3200.0 (libva 1.0.14 as of today)
VA-API 0.34.1 generates libva.so.1.3401.0 (e.g. libva 1.2.1)
VA-API 1.2.13 generates libva.so.2.213.0  (e.g. libva 2.2.13)

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>