print_help print an usage message from an OptionParser object, usually called by parse_args when it encounters a help option.
print_help
parse_args
print_help(object)
print_help uses the cat function to print out a usage message. It returns invisible(NULL).
cat
invisible(NULL)
A OptionParser instance.
OptionParser
Trevor Davis.
Python's optparse library, which inspired this package, is described here: https://docs.python.org/3/library/optparse.html
optparse
{parse_args} {OptionParser}
{parse_args}
{OptionParser}