Added one_small_row, one_big_row, many_rows, stmt_params benchmarks against libmysqlclient and libmariadb
Added a CI build to compile and run benchmarks
Added a Python script to run the benchmarks
Refactored the connection_pool benchmark to be use data independent from examples
close#458
All test targets (including integration tests) are now only built when
the `tests` target is built.
Added a CMake build that doesn't run integration testing (verifying that
BOOST_MYSQL_INTEGRATION_TESTS works)
close#261