Rails 3 support

[Andrew France]

Hi everyone,

I've received one report of a Rails 3 incompatibility problem due to
ARel defining a global Table() method:
https://github.com/ruport/ruport/issues#issue/3

Polluting the global namespace isn't great anyway and I've moved our
Kernel.Table() convenience method to the Ruport module. So the
equivalent functionality can be had by "include Ruport" or
Ruport.Table(), but I will probably note in the documentation that the
method as deprecated in favour of Ruport::Data::Table.new and friends.

As this is a backwards incompatible change, it'll require a minor
version increase from 1.6.3 to 1.7.0. Before I do that I'd welcome any
reports of Rails 3 problems (or any other issues!) before I release it
in a week's time.

Regards,
Andrew