Default values were not set for options in groups, updated OptionParser to also set default values for groups.
Default values were not set for options in groups, updated OptionParser to also set default values for groups.

weisslj/cpp-optparse,dm0/cpp-argparse,weisslj/cpp-optparse,dm0/cpp-argparse,weisslj/cpp-argparse,dm0/cpp-argparse,weisslj/cpp-optparse,weisslj/cpp-argparse,weisslj/cpp-argparse