This is needed for examining the values of user counters (needed
for #348). It is also needed for checking the values of standard
benchmark results like items_processed or complexities (for example,
checking the standard deviation is needed for unit testing #357
as discussed in #362).
* refactor
* Move default substitutions into library
* Move default substitutions to the *right* place in the library
* Fix init order issues that caused test failures
* improve diagnostics
* add missing include
* general cleanup
* Address review comments