Add an option to dms::to***String() to produce machine-readable strings

It's often convenient to have a string of the format HH:MM:SS or
[-]DD:MM:SS for processing, as it is awkward to have unicode degree
symbols etc in ASCII strings. Therefore, it's nice to have
dms::to***String() have a machineReadable option to produce
machine-readable strings instead of human-readable ones.