Pull more external codelists from their source programmatically

[Bjwebb]

IANA

• [x] File Format - https://github.com/IATI/IATI-Codelists-NonEmbedded/issues/7 - http://www.iana.org/assignments/media-types/media-types.xhtml

ISO

• [x] Country - http://www.iso.org/iso/home/standards/country_codes.htm [requires paying for the Online Browsing platform]
• [x] Currency - http://www.iso.org/iso/home/standards/currency_codes.htm
• [ ] Language - http://www.iso.org/iso/home/standards/language_codes.htm https://github.com/IATI/IATI-Codelists-NonEmbedded/issues/8#issuecomment-72883166

US NGA codes have been split into a separate issue https://github.com/IATI/IATI-Codelists-NonEmbedded/issues/53

DAC codes have been split into a separate issue https://github.com/IATI/IATI-Codelists-NonEmbedded/issues/52

[Bjwebb]

List of all changes can be found at http://www.loc.gov/standards/iso639-2/php/code_changes.php. No changes to the two letter codes have occured since IATI first started using this codelist. Therefore, I don't think it's important to be able to pull this list programmatically.

[Bjwebb]

This should be fixed when https://github.com/IATI/IATI-Codelists-NonEmbedded/pull/51 is merged.