add volk_version.h

[michaelld]

subject says it all. standard CMake substitutions. resulting VOLK_VERSION will be in the format MAMIMT: MA == major; MI == minor; MT == maint; any will have a preceding 0 if the number is otherwise a single digit (e.g., MA of "2" will result in "02" here, but "11" will just be "11"). This is the same style as done by Boost and other projects, since it makes for simple macro-based comparisons in C / C++ code.

Closes: #338

[michaelld]

This change should be sufficient for GR, e.g., for the broken rotator in 2.0 that we fixed in 2.1.

[jdemel]

This PR looks good. But there are a few minor things.
Mostly, the question arises if volk_version.h should be included in volk.h. volk_malloc.h etc. are included and I'd prefer to add this header as well.

[michaelld]

Mostly, the question arises if volk_version.h should be included in volk.h. volk_malloc.h etc. are included and I'd prefer to add this header as well.

I had thought this too, but decided to not for the initial PR. I think since volk.h includes all of the headers except volk_vector.hh, it should also include this one. I'll add it.

[michaelld]

volk_version.h is now included in volk.h

[michaelld]

@marcusmueller do you think the PR's addition (volk_version.h) is sufficient for what GR needs, per our recent discussions?

[jdemel]

LGTM

[michaelld]

Hoping to get an approval from at least 1 GR dev here ... so I tagged a few!