This function is used to create an instance of a parser object
which when combined with the parse_args, make_option, and add_option
methods is very useful for parsing options from the command line.
OptionParser(
usage = "usage: %prog [options]",
option_list = list(),
add_help_option = TRUE,
prog = NULL,
description = "",
epilogue = ""
)The program usage message that will printed out if
parse_args finds a help option, %prog is substituted with the
value of the prog argument.
A list of of OptionParserOption instances that will
define how parse_args reacts to command line options.
OptionParserOption instances are usually created by make_option
and can also be added to an existing OptionParser instance via the
add_option function.
Whether a standard help option should be automatically
added to the OptionParser instance.
Program name to be substituted for %prog in the usage
message (including description and epilogue if present),
the default is to use the actual Rscript file name if called by an
Rscript file and otherwise keep %prog.
Additional text for print_help to print out between
usage statement and options statement
Additional text for print_help to print out after
the options statement
An instance of the OptionParser class.
Python's optparse library, which inspired this package,
is described here: http://docs.python.org/library/optparse.html