Implemented Joi validation/toJSONSchema with legacy fallback. See #926.
Implemented Foxx model auto-validation with joi.
Don't clone objects just to throw them away.
Added documentation for errors and isValid.
Docs consistency.
Adjusted Foxx Model docs to use joi instead of legacy schema.
Fixed typo.
Clarified isEmpty check.
Marked old Model.extend syntax for deprecation.
Fixes false positioning of edge #894. Tested  in FF, Chrome, Safari, IE11 (all newest versions)
Merge branch 'devel' of github.com:triAGENS/ArangoDB into devel
Merge pull request #932 from triAGENS/foxx-joiful-models

Use Joi for model validation (fixes #926)
Made Foxx RequestContext bodyParam more consistent with other param methods. Fixes #935.
Added tests.
Undocumented body param now uses new syntax.
Added old requestContext.bodyParam to DEPRECATED.md.
Removed deprecation warning for now.