fetch_series.m

Clarify documentation:

• replace strjoin as it's only supported in R2013a and later
• The phrasing "If not None, ..." implies that key is required and that you must pass 'key', 'None' to turn it off.
• It would be useful to have a list of keys, clearly describing what they are for and what values they accept. The form this takes is up to you, it should just be done clearly. It would also be useful to know which keys are required, which are optional, and which are required when another key is passed. Keep in mind how this displays when you type help fetch_series at the MATLAB command.
• if dimensions is not a function_handle and series_code is provided, series_code takes precedence over dimensions. Is this desired? Should an error be thrown if both of these are passed to make it explicit to the user?
• These two examples from the header don't work:
  • fetch_series('provider_code', "IMF", 'dataset_code', "CPI", 'series_code', "M..PCPIEC_IX+PCPIA_IX")
  • fetch_series('provider_code', "AMECO", 'dataset_code', "ZUTN", dimensions={"geo": ["dnk"]})