Couple of things:
- No need to use string streams to format the version string,
we can do it at compile time and don't bother with anything
at runtime.
- Function declaration was wring and would have caused linking
conflicts in cases when util_version.h was included from
multiple places.
We should have an utility function to get Cycles version so
applications which are linked to Cycles dynamically can query
the version, but that can't be done as an inlined function in
header and would need to be a function properly exported to a
global symbol table (aka, be implemented in a .cpp file).
Now Cycles has its own versioning, that is mainly interesting for external projects, which integrate the engine.
We start with version 1.7.0. Reasons for that:
* The engine is too mature for a 1.0 release.
* We assume that Cycles inside of Blender 2.61 was version 0.1. We count upwards in 0.1 steps, therefore Cycles inside of Blender 2.77 would be 1.7.
We use a common versioning scheme here, with 3 decimals for the major, minor and patch level.
At the moment cycles --version can be used to display the version, easy to parse for external projects. The info will be added to the UI later aswell.
