Closes #60

This is needed to be able to use (for instance) constant references to these
constants in user code in C++14 mode. In C++17 mode the explicit declaration
is not needed anymore. But it also doesn't hurt the compilation.

Closes #59

Gitlab CI authored 6 years ago and Marco Clemencic committed 6 years ago

patch generated by standalone job

- do not rely on LCG clang-format installation
- do not require cmake configuration

Closes #57

* introduce CounterHolder, which keeps track of the
  available counters, and provides declareCounter,
  findCounter, forEachCounter, nCounters and clearCounters

Closes #54