indexing bounds checking

Fixed #102, other issues found, tests added
clean up 2-index error checking.

some raise a "not implemnted" eroor.  Some issuees uncovered, needs
work.
index fixes: empty index b([], []) was failing
indexing: fixes for matrix(vec), vec(matrix=0, etc, clean code

Fixes #113.
indexing: fix empty access to correct sizes, alkow ''

octave has x('')bsame as x([]). do that too.
Merge pull request #115 from cbm755/fix_102

Fix 102, "x(1,1)" error, other indexing improvements