Move POD to the bottom of Test/Kit2.pm
Explain the Test::More::TODO hack in the POD
No need to 'use Exporter'
Use 'use parent' over 'use base' for Exporter

As per the documentation for 'use base', which suggests using 'parent'
unless the 'fields' pragma is in use.
Don't hard-code the package name, use $class

_get_package_to_import_into() had the package name Test::Kit2 hard-coded
in it when it could just use the $class variable.

This is mostly important if people want to sub-class Test::Kit2.
Add test/example code for sub-classing Test::Kit2

Sadly because Perl only allows inheritance of subroutines and not
variables, and because Exporter requires @EXPORT to be set in order for
it to export anything, sub-classing is not as simple as

    use parent 'Test::Kit2'

But it's not too complicated at only three lines

    use Test::Kit2;
    use parent 'Test::Kit2';
    our @EXPORT = @Test::Kit2::EXPORT;

:-)