* Lots of clang-tidy fixes

This enables a bunch of clang-tidy rules, and fixes nanobench.h wherever
possible, and otherwise disables the warning at that line.

* Updated documentation, adding missing files

Also update highlighting locations

* only use W4 warnings for MSVC

* Check for failures in parseFile()

Check for failures when opening/reading the CPU frequency related sysfs
files, to avoid needless warning messages.

Note that if `scaling_min_freq` and `scaling_max_freq` both fail, then
`minFreq` and `maxFreq` will be zeroes and no warning is generated.

* Fallback to PERF_COUNT_HW_CPU_CYCLES

Not all platforms support the reference cycles, so fallback to the cycle
counter, it's better than nothing.

* Add HW perf events before SW events

The mixed order of HW and SW events causes EINVAL failures from some of
the perf_event_open() syscalls in one embedded device with 4.14 kernel.
Fixed by adding all the HW events first, then the SW events.

Due to GCC/libstdc++ bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58265
the string move assignment may be missing noexcept, resulting in build
errors even with relative recent GCC versions:

```
nanobench.h:2898:9: error: function 'ankerl::nanobench::Config& ankerl::nanobench::Config::operator=(ankerl::nanobench::Config&&)' defaulted on its redeclaration with an exception-specification that differs from the implicit exception-specification ''
 Config& Config::operator=(Config&&) noexcept = default;
         ^~~~~~
```

* update a bunch of links

* use the little d() helper instead of static_cast<double> where possible

* add lots of nodiscard

* add missing noexcept (g++ complains)

std::string(std::string&&) is noexcept since c++11

Fixes #118.