tests: remove CLRF line endings

Use the "dos2unix" command to adjust the line endings.
tests: remove trailing whitespace
tests: switch to minitest

Ruby 1.9+ uses Minitest as the backend for Test::Unit. As of Minitest 5,
the shim no longer supports Test::Unit::TestCase.

Adjust the geoip test suite to support Minitest 5's syntax.
tests: add simple constructor test

Create a new GeoIP object, and verify that it's an instance of GeoIP.

If GeoIP.dat is unavailable, skip the test.
tests: add support for Minitest versions < 5

Minitest versions 4 and below do not support the newer Minitest::Test
class that arrived in version 5. Use MiniTest::Unit::TestCase as a
fallback.
Merge pull request #46 from ktdreyer/tests

improve test suite