This change modifeis Options.hpp to add the possibility of
vector-valued options to the config file and command line.
From the 'case' code, this option is used by (for example)

std::vector<int> intvec;
add_option("Name",&intvec,"Description);

When run, options of the form --Name 1 2 3 4 (at the command
line) or Name = 1 2 3 4 (in the config file) will be added
to the vector 'intvec' as separate entries.

Because add_option is a template function, this works
identically for double (floating point)-valued options.  It
has not been tested with string options.

Since an empty vector is a perfectly cromulent and
unambiguous possibility, vector-valued options do *not*
permit the specification of defaults.