Release v1.0.0

What's changed

Bug fixes:

• Issue with downloading multiple series in a single function call (i.e. specifying input 'fred_code' as a vector containing multiple mnemonics) has been fixed.

Updated features:

• Input 'fred_code' can be of any supported class: char, string (array), cell (array of chars). Previous version was not supporting a cell input.
• Invalid mnemonic codes (i.e. mnemonics that do not correspond to any series in the FRED database) return a warning but do not stop the execution of the function. This allows the function to ignore any invalid mnemonics but downloads all valid ones specified in 'fred_code'. Previous version was returning an error (and therefore, was stopping function execution).