Old definition was using the class keyword, the new one was initially using struct and so any forward declaration created a clang warning.
We are now back to class.

* master:
  Add test and fix of version propagation in KeyedContainer move (#27)

This avoids problems when the user has GIT_DIR and/or GIT_WORK_TREE set
in the parent shell.

Closes #27

* master:
  Fix changes list for formatting check

The new counters have a few new features compared to existing StatEntity :
  - they are templated by the counted type
  - they come with different flavors counting only what you need (e.g. simple count, no stat)
  - more flavour can easily be created at will thanks to the AccumulatorSet object
  - they come with 2 implementations : thread safe or not
  - the thread safe ones use atomics and should be as efficient as possible
  - a Buffer object allows to easily buffer updates to a counter made in a tight loop, without paying the atomic price each time

A Small unit test is available in the test suite and example code is provided in the comments of Counters.h where they are implemented.
Existing code has been adapted, in particulat the ChronoSvc.

Closes #17

Closes #22

Fixes gaudi/Gaudi#22