In order to make the support for different Elasticsearch versions more clear,
a special "Compatibility" chapter has been added to the main README and
individual gem READMEs.

The versioning scheme follows the scheme for the Elasticsearch Ruby client,
ie. the version number matches the supported major version of Elasticsearch.

See:

* elastic/elasticsearch-ruby@3bdb385

Related: #693

…-model" to `5.x`

Related: #693

The 5.x versions should depend on the corresponding version of the Ruby client.

Related: #702

…o_save` for compatibility with Rails 5.1

Without this patch, the log on Rails 5.1 is full of deprecation warnings like:

    DEPRECATION WARNING: The behavior of `changed_attributes` inside of after callbacks will be changing in the next version of Rails. The new return value will reflect the behavior of calling the method after `save` returned (e.g. the opposite of what it returns now). To maintain the current behavior, use `saved_changes.transform_values(&:first)` instead. (called from update_funding_caches at...

It was first reported in #714.

This patch fixes #758.

…k with older Rails versions

This patch builds on work in #738 by @jkeam and #758 by @Geesu to prevent deprecation warnings on Rails 5.1
due to changes in the handling of "changed attributes", originally reported by @davedash in #714.

It's primary focus is to restore the compatibility with older Rails versions (so we don't break compatibility
without proper version bump and in a single isolated commit), and to make the naming a bit more descriptive.

First, the condition has been changed to work with the `changes_to_save` and `changes` methods, as opposed
to the original `changed_attributes` / `attributes_in_database` naming. This communicates much more clearly
the intent, and the original usage of `changed_attributes` has been misleading.

Also, the "internal instance variable" which keeps track of the changes has been renamed to `@__changed_model_attributes`,
in order to cleary differentiate it from the `changed_attributes` method name in older ActiveRecord versions.

Closes #758

* [CI] Update Travis matrix

* [MODEL] Mock the #to_ary method in multimodel test for Ruby 2.2

…809)

…Mongoid (#786)

* [MODEL] Support scope, query and preprocess importing options in Mongoid Adapter

* test(mongoid-adapter): add testing for importing mongoid model with default scope