Bblocks

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- Update WFP data handling to append new data instead of replacing.

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- WEO update file path bug fix.

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- Minor bug with file management resolved.

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- Added an optional parameter to importers in order to specify where the data should be stored.

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- Fixed how the ``WorldEconomicOutlook`` object handles moving to the latest data
- Added new optional parameters to ``WorldEconomicOutlook`` to allow for
specifying the data version.
- ``WorldEconomicOutlook`` now has an instance attribute ``version`` that
stores the version of the data used to create the object.

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- Added a new feature: ``date_to_str()``, which formats a date as an english string.
- Added a new feature: ``format_number``, which formats a numeric series as a formatted string (e.g. 1,234,567.89
instead of 1234567.89). Optionally can specify to format as percentage, millions, or billions.
- Added a new feature: ``latest_sdr_exchange``, which extracts the latest SDR exchange rate information in a dictionary
- Fixed bug on SDR object - when ``update_data = True`` indicators are loaded in the object when
``load_indicator`` is called.