Changes done to Nonius:
* Moved things into "Catch::Benchmark" namespace
* Benchmarks were integrated with `TEST_CASE`/`SECTION`/`GENERATE` macros
* Removed Nonius's parameters for benchmarks, Generators should be used instead
* Added relevant methods to the reporter interface (default-implemented, to avoid
breaking existing 3rd party reporters)
* Async processing is guarded with `_REENTRANT` macro for GCC/Clang, used by default
on MSVC
* Added a macro `CATCH_CONFIG_DISABLE_BENCHMARKING` that removes all traces of
benchmarking from Catch
Xml result of reported will now contain value of rng-seed in case it
is not zero.
The value will be stored in element Randomness and it's attribute seed.
Relates to #1402
By opting the JUnit and XML reporters into it, we no longer run
into problem where they underreport the results without `-s` flag.
Related to #1264, #1267, #1310