Merge test suite from original repository

[myint]

There hadn't been much activity the last time I checked. But there is an interesting test suite that uses the Python optparse as ground truth:

https://github.com/weisslj/cpp-optparse/commit/f95e9433f1751eff52ab5a5af55dcaa05529e6b4#diff-1b531c5e405e0bc95890d52cf2f2f5b5