Issue #83 Updated record_string to correctly escape quotes and backslashes 

...when turning the datashape into a string.

This fixes a problem in blaze where converting from one datatype to another would throw errors when transferring the datashape from one source of data to another.
Several tests have been added and all tests pass.
I think this is an error in the datashape grammar specification, I don't see a reason to exclude this case.