demonstrate ZMP tracking error
more accurate labeling of tests
experimental support for non-unit costs in ZMP closed form
update closed ZMP solution to support non-unit costs, and add tests
only check size along first dimension
clean up
make sure frame_id is the right shape (column, not row)
handle R2012b missing flip() command
Merge pull request #619 from rdeits/rd-test-zmp-tracker

Clean up and clarify ZMP closed-form solution