Introduce #paranoia_destroy_attributes and #paranoia_restore_attributes extension points

Use update_columns rather than touch to update the record, for
generality

Unlike touch, update_columns does not create a transaction for
itself, so we need to add the record to the transaction, if present.
If there is not a current_transaction, the add is a no-op.

This all means that delete will not invoke a transaction or run the
after_commit callbacks unless called from within one, which is
consistent with the Rails docs and the behavior of
ActiveRecord::Base#delete.

Fix uniqueness validator for non-paranoid associations

real_destroy callback

Fix for #122, #121 and #175 on Rails 4 branch

Ruby 1.9's version of `Object.const_get` does not support namespaced constants, so this commit replaces it with `ActiveSupport`'s `#constantize` method.

The tests were failing running JRuby on 1.9 mode. CRuby was not failing because it is not tested against 1.9.

Fixes #114

Fix association class name for namespaced has one model lookups

Use association.klass.name instead of association.class_name to get the
namespaced class name and therefore prevent:

`Object.get_const(association_class_name)`

from raising "uninitialized constant ParanoidHasOne"
in the following situation:

module Something
  def self.table_name_prefix
    "something_"
  end

  class ParanoidHasOne < ActiveRecord::Base
    acts_as_paranoid
    has_one :paranoid_belongs_to, dependent: :destroy
  end

  class ParanoidBelongsTo < ActiveRecord::Base
    acts_as_paranoid
    belongs_to :paranoid_has_one
  end
end

hasOne = Namespaced::ParanoidHasOne.create
hasOne.destroy
hasOne.restore(:recursive => true) # previously would explode

add GoRails video to readme documentation

Fix typo

partial indexes advice

Update README.md

Remove table_name from where methods

Show the 'restore' instance method also in the code snippets

- `client.restore`
- `client.restore(:recursive => true)`

Fix counter cache behaviour on rails 4.2

This has been removed and should no longer exist.
https://github.com/radar/paranoia/pull/192#discussion_r24884921

I asked about `restore` in the
[Notes](https://github.com/radar/paranoia/pull/192#issue-51914917) of
the PR's description. Personally I don't need such a behaviour. So
removing.

remove unused parameter

This will allow to detect counter cached columns changes in callbacks
like `after_destroy` or `after_commit on: :destroy`.

My goal is Rails 4.2 support and it works well with Rails 4.2. I’m
leaving this bug not fixed for Rails 4.1 for the time being.