[QUANTITY] why we should have string values in quantity

[Jonathan McDowell]

Brian and Ray,
 Just for the record, and I probably have said this already, the
real reason I want to see Q support strings is because I already
have a lot of software that operates on things very like a Q which
includes string-valued things. Indeed, in my mind Q is something
which can be used to represent FITS keywords and FITS table columns,
both of which are objects which are very like our discussions of Q
and which one often wants to perform metadata operations on independent
of whether they are string or numeric valued. This real world 
situation - that the thing in our data now which most closely maps
to Q is something which can be either numeric or string valued and
which shares common metadata and methods - convinces me that having
Q support strings, even though some of the other things like error etc
will be unused in that case, is more convenient than having two separate
classes. 
 I further submit (pace Gerard) that not all strings are classifications;
sometimes it can be formatting (sexagesimal positions) and sometimes
descriptions, among probably other cases.

  Jonathan