Modifed handling of match failed info in summary.optmatch and print.summary.optmatch.
If I am correct that a subproblem has only NAs for its match IDs if and only if matching failed for that subproblem, then these changes should lead to correct reporting on the extent of match failure (as distinct from leaving units unmatched.)
Implemented / and * for ISMs w/ vectors
Made vector arith more general; added replication for vectors to mimic matrix/vector arithmetic
Docs for `print.optmatch`. User must type ?print.optmatch

Closes #53.
forgot to add print.opmatch examples file, fixes #55
tests for getting correct subgroup failure indicators
updating tests to new matching.failed format
noticed a warning related to the changes to match.failed attrib, updated R CMD check save file
Merge branch 'matchfailed-omission'
Merge branch 'ism-vector-arith'
Merge branch 'master' of https://github.com/markmfredrickson/optmatch into rank.mahalanobis
initial unit test for compute_rank.mahal