nadaverse 0.2.0

New features

Added three catalogs: the Kenya National Bureau of Statistics ("kenya"), the World Health Organization Health Information Systems survey catalog ("who"), and the Zambia Statistics Agency ("zambia").
New set_user_agent() sets the user agent sent with requests. The default is a browser user agent, which UNHCR requires.
Requests now time out after 30 seconds and are attempted up to three times, including after connection errors.
A catalog that replies with something other than JSON, such as a block page, now stops with a clear error message.

Removed the "ilo" and "india" catalogs. The ILO survey catalog has been retired, and the Government of India catalog could not be reached when testing.