Cleanup

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Support for warmup, to ignore the first n measurements from the same benchmark invocation

This closes #15.

Note, tests now include a `features` folder for the test cases for such additions.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Made cli_options optional

Signed-off-by: Stefan Marr <git@stefan-marr.de>