Python 3 fix and documentation updates

* The description for `org_by_name` incorrectly directed people to use
  `name_by_addr` rather than `name_by_name`.
* Previously `GeoIP.country_names` was populated from `GeoIP_country_name` in
  the libGeoIP C API. Some versions of the libGeoIP include non-ASCII
  ISO-8859-1 characters in these names, causing encoding errors under Python
  3. When installed under Python 3, this API now uses UTF-8 country names to
  populate this dict. Reported and fixed by Sergey Farbotka. GitHub PR maxmind#15.

Fix for broken strings in Python 3.

Strings with non-ASCII characters would throw a UTF-8 decoding error.
In Python 3, all strings from the database are in UTF-8 and using
`set_charset` to set the character set to something other than UTF-8
will throw an `ValueError` exception.

Python 3 support

* Python 3 support and significant code cleanup. ( Zack Weinberg )
* The methods `name_by_addr`, `name_by_addr_v6`, `name_by_name`, and
  `name_by_name_v6` were added for ISP, Org, and ASNum lookups.
  ( Carlos Rodrigues )
* Portability fixes.
* Expose `GEOIP_MMAP_CACHE` from the C library. ( George Macon )
* Unit tests were added.

Packaging fix. PyPI-only release.

Release 1.2.8

Add netspeedcell example

Add new methods record_by_name_v6 and record_by_addr_v6 to support Ge…

…oIPCityv6 databases. ( Boris Zentner )

Release 1.2.5