Basic support for array-of-structs in options

Basic support for array-of-structs in options

This makes it possible to parse structured data that has
arrays-of-struct type of constructs (as long as the structure for the
array elements is reasonably uniform).  Iteration over the sections does
not work reasonably for these types of sections yet, and there are other
things that might not work.  For complicated nested data structures,
there is also some unnecessary copying.  But the tests show that basic
stuff does work.

Change-Id: Ib485248a5adabecc3ed126dfa3736a5e71577bfd