Drop DataMapper support

it looks like DataMapper 1.2 is no longer maintained:

  * https://groups.google.com/forum/#!topic/datamapper/iTqd6IGxXpA
  * https://groups.google.com/forum/#!msg/datamapper/UCHC5TF6I0M/HamsbyNxuVAJ

0.16.x will still have support for it, but not in 1.0.0.
Drop ActiveRecord 3.0/3.1 support

But 0.16.x will still have support for them.
Fix the test suite for mongoid 40

It didn't run due to:

  moped-2.0.2/lib/moped/cluster.rb:254:in `with_primary':
    Could not connect to a primary node for replica set #<Moped::Cluster @seeds=[<Moped::Node resolved_address="127.0.1.1:27017">]>
    (Moped::Errors::ConnectionFailure)
Fix mongo mapper test suite

https://travis-ci.org/amatsuda/kaminari/jobs/41827391#L98
Drop support for MongoMapper.

This extension will be unsupported in Kaminari 1.x

If you'd like to support it, please let us know by opening a ticket on
https://github.com/amatsuda/kaminari/issues/new

Conflicts:
	.travis.yml
	README.rdoc
	spec/fake_app/mongo_mapper/config.rb
Remove support for mongoid 2.4 and 3.x

Conflicts:
	.travis.yml
Drop support for Sinatra 1.3, only support Sinatra 1.4.x
Remove old rake tasks