added requirements
use lookup_url_kwarg as intended
use mongoengine get_document_or_404 instead of regular django shortcut
UUID field mapping
keep fields ordered on serialization
return None if EmbeddedDocument is None
Output pk of object if exist, when depth has exceeded
unmapped fields default to WritableField
solved the issue where dynamic fields defaults to string
preserve order on EmbeddedDocument serializing
Merge remote-tracking branch 'remotes/drf-original/master'

Conflicts:
	rest_framework_mongoengine/fields.py
	rest_framework_mongoengine/generics.py
	rest_framework_mongoengine/serializers.py