unification of meta-attributes handling:
* remove has_format, has_text_encoding, format, text_encoding methods on Entity
* remove rich_text_fields method on EntitySchema
* use instead has_metadata / meta_attribute on EntitySchema (from yams)
and attribute_metadata on Entity
def postinit(vreg):
"""this callback is called at the end of initialization process
and can be used to load explicit modules (views or entities).
For instance :
import someviews
vreg.load_module(someviws)
"""
# from migration import migrate
# migrate(vreg)