There is a unused parameter at benchmark:866 Benchmark::MeasurePeakHeapMemory .
The function is marked as TODO and the code that uses the parameter is commented out.
I just removed the parameter so it can compile again without editing the CMake compile flags.

Fix cycleclock.h for gcc/ARM.

Currently there are tests for ARMV3 and ARMV6 in cycleclock.h which are not
defined using gcc on ARM. Since there is also a cast to the unknown type
int64 I assume that the ARM code has not been tested. Therefore this patch
replaces the checks for ARMV3 and ARMV6 by checks for __ARM_ARCH. Also, the
cast to int64 is fixed by casting to int64_t.

Ensure families is not nullptr before using it

When there's no benchmarks, families becomes nullptr. So before touching
it, we need to ensure families is not nullptr.

Update README.md

Inspired from the one from https://github.com/google/go-github.

Switched to language specific markdown for code sections to provide syntax highlighting when rendered.

Cmake edit with 'make install' target

Fix int64_t_t typo in README code example

Fixes a typo where the first type was written as int64_t_t with suffixing _t twice and the second type misses suffix at all.

Ensure we run at least 1 iteration.
Take into account overhead of an empty benchmark.
Minor cleanup of code.