Make end-of-options delimiter configurable

[remkop]

Related to #358.

Currently, the -- (double hyphen) token is the hardcoded end-of-options delimiter. When this token is encountered the remaining command line arguments are treated as positional parameters.

This ticket is to make the end-of-options delimiter configurable. This allows:

• a different string as the end-of-options delimiter
• treating -- as a normal token, so applications can have an option named ”--“ or capture this token in a positional parameter