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.

This is a workaround actually. Since
`ActiveRecord::CounterCache.each_counter_cached_associations` is
private. We shouldn’t use it. Proposals for the proper fix are welcome.

The reason the previous version stopped working is `affected_rows`
returns `0` at
[active_record/counter_cache.rb#L142](https://github.com/rails/rails/blo
b/ef99d4cd3ecc58a8c1484740b2fb5447dbda23ab/activerecord/lib/active_recor
d/counter_cache.rb#L142). If you follow the method call you’ll find
that it’s called at
[active_record/persistence.rb#L486](https://github.com/rails/rails/blob/
ef99d4cd3ecc58a8c1484740b2fb5447dbda23ab/activerecord/lib/active_record/
persistence.rb#L486). Probably we’d better override the return value in
`ActiveRecord::Relation.delete_all` at
[active_record/relation.rb#L481](https://github.com/rails/rails/blob/ef9
9d4cd3ecc58a8c1484740b2fb5447dbda23ab/activerecord/lib/active_record/rel
ation.rb#L481).

https://github.com/radar/paranoia/blame/1b051ae78793f3b62297b5adbaa9c1d0
0e6726e0/README.md#L154

http://edgeguides.rubyonrails.org/4_2_release_notes.html#active-record-d
eprecations
> Deprecated passing Active Record objects to .find or .exists?. Call
id on the objects first.
Commits in Rails:
https://github.com/rails/rails/commit/d92ae6ccca3bcfd73546d612efaea01127
0bd270
https://github.com/rails/rails/commit/d35f0033c7dec2b8d8b52058fb8db495d4
9596f7
https://github.com/rails/rails/commit/c0609dd0f0f0de604ac1ffeffdf5e3e0e7
356b35

Update README about rails3 branch

Update README.md

Add a mention for https://github.com/radar/paranoia/issues/109#issuecomment-74455252

I think this advice is misleading for most datasets and most RDBMS this
is not necessary, and as per #206 doesn't even work.

I have moved it to the wiki
https://github.com/radar/paranoia/wiki/Custom-sentinel-values

This is a test for a case when a model has a has_one association with an
after_validation callback, and we have failed validation. Paranoia will
attempt to touch the deleted_at column on the child record that has
been built but not saved.

Fixes #180

This allows testing rails 4.0 on ruby 2.2

We no longer have different behaviour between AR versions.

We shouldn't be overriding this. soft-deleted objects are still
persisted.

The default implementation is already destroy || raise

Thanks @kidlab