Added a CONTRIBUTING guidelines document.
Use default_error_status to specify the default status code returned from error\!.
The default status code returned from error\! has been changed from 403 to 500.
Merge pull request #525 from dblock/default-error-status-500

Default error status 500
Allow specifying headers in error.
Aliased before as before_validation.
Make before_validation its own distinct callback
Fix: calling declared(params) from child namespaces fails to include parent namespace defined params.
Merge pull request #527 from myitcv/before_validation_callback

Make before_validation its own distinct callback
Fix example code in README.md

To upload file, `curl` requires `@` at the beginning of file path.
Merge pull request #532 from tricknotes/fix-example-in-readme

Fix example code in README.md
Helpers are now available to auth middleware, executing in the context of the endpoint.
Fix rescue_from example
Merge pull request #536 from styx/patch-2

Fix rescue_from example
added failing spec: default values for grouped parameters
Fix default values for grouped params
Merge pull request #538 from dm1try/fix_default_values_for_group_params

Fix default values for group params
Pull grape-active_model_serializers into new section in readme
Merge pull request #539 from jrhe/master

Mention grape-active_model_serializers in readme
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Pull grape-active_model_serializers into new section in readme
  Fix default values for grouped params
  added failing spec: default values for grouped parameters
  Fix rescue_from example
  Helpers are now available to auth middleware, executing in the context of the endpoint.
  Fix example code in README.md
  Fix: calling declared(params) from child namespaces fails to include parent namespace defined params.
  Make before_validation its own distinct callback
  Aliased before as before_validation.
  Allow specifying headers in error.
  The default status code returned from error\! has been changed from 403 to 500.
  Use default_error_status to specify the default status code returned from error\!.
  Added a CONTRIBUTING guidelines document.