Descriptive API error messages

[c-zippel]

The program can't show descriptive error messages if the Census API does not return data, because it parses the JSON response as a delimited text file (and uses string functions to take out the brackets and quotes). Hence, if the API response is not parseable as a delimited text file (i.e. an error message is returned instead of data), then the resulting data will be empty and the program will exit (r(N) == 0).
My proposed solution, short of changing how the program parses the JSON so it has more flexibility to pass on error messages from the Census, is to:

• Always return a link to the API call (see issue Display link to API call instead of text #1 ) so that users can click it to view the error message in their browser; and
• Expand the current error message to include more reasons why the API call could have failed

[c-zippel]

okay, unlike most APIs census doesn't return error messages in the JSON; they're in the header which Stata can't read. so best we can do is the options in bullets, both of which implemented in dev version

[c-zippel]

issue superceded by #37