Change :embed_key to :key
Allow default namespace inheritance
Fix default serializer option
Default serializer tests

Based on namespace serializer tests except namespace is set in
default_serializer_options
Changelog: Default serializer option
typo
Fix meta_key/meta documentation

This updates the documentation to reflect the behavior implemented by
the v0.9.x series. Note that this behavior differs from that of the
v0.8.x series, which is reflected by the current documentation.

Consideration should be given to patching the v0.9.x series to revert
back to the v0.8.x behavior since I'm not entirely sure if this slight
change was intentional, but for the time being, this at least documents
the existing behavior correctly.
Make sure `render json: ..., each_serializer: ...` is working with Enumerables

If you try to render Enumerable with custom `each_serializer` then it will render with default serializer instead:

```ruby
render json: sequel_scope, each_serializer: CustomSerializer
```

This commit fixes this behaviour. Most likely fixes https://github.com/rails-api/active_model_serializers/issues/664 as well
Merge pull request #665 from andreychernih/fix-each-serializer-option

Make sure `render json: ..., each_serializer: ...` is working with Enumerables
Merge pull request #634 from craiglittle/fix-meta-documentation

Fix meta_key/meta documentation for v0.9.x series
Merge pull request #632 from gauthier-delacroix/Default_namespace_inheritance

Default namespace option
Merge pull request #630 from sachse/readme-fix

README: Change :embed_key to :key
Add auto-stripping of question mark for attributes
Merge pull request #662 from jastkand/remove-question-sign

Add auto-stripping of question mark for attributes