benchmark

Add possibility to ask for libbenchmark version number (#1004) (#1403)

* Add possibility to ask for libbenchmark version number (#1004)

Add a header which holds the current major, minor, and
patch number of the library. The header is auto generated
by CMake.

* Do not generate unused functions (#1004)

* Add support for version number in bazel (#1004)

* Fix clang format #1004

* Fix more clang format problems (#1004)

* Use git version feature of cmake to determine current lib version

* Rename version_config header to version

* Bake git version into bazel build

* Use same input config header as in cmake for version.h

* Adapt the releasing.md to include versioning in bazel