This updates the "lookup_location" and "lookup_asn" BIFs to use
libmaxminddb. The motivation for this is that MaxMind is discontinuing
GeoLite Legacy databases: no updates after April 1, 2018, no downloads
after January 2, 2019. It's also noted that all GeoIP Legacy databases
may be discontinued as they are superseded by GeoIP2.
Updated the install section for FreeBSD and OS X.
Added a section to explain how to quickly test that everything is
setup correctly.
Improved the usage section by removing the misleading record definition
(a link to the reference doc is provided), and explaining that some
fields will be uninitialized.
Corrected the example so that it doesn't try to access uninitialized
fields.
Added a few missing packages to the install instructions.
Combined the two different sets of GeoIP install instructions into one
location and updated it.
Fixed a couple minor typos.
