ecb 0.4.4

• All functions that query the ECB Data Portal now fail gracefully, as required by CRAN policy. If the API cannot be reached, returns an HTTP error, or returns a response that cannot be parsed, an informative message is shown and NULL is returned invisibly instead of throwing an error.
• Requests now use a default timeout of 60 seconds, which can be overridden by passing httr::timeout() through ....
• get_description() gains a ... argument passed on to httr::GET().
• get_data() now passes ... on to get_dimensions() when detail is "serieskeysonly" or "nodata".
• convert_dates() returns zero-length input unchanged.
• Examples that access the internet are wrapped in \donttest{}, and the vignette skips code that depends on downloaded data if the API is unavailable.
• Added offline tests; online tests now skip if the API is unavailable.