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

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.