Content migration utilities  
by Martin Aspeli <optilude@gmx.net>

Released under the GNU Lesser General Public License (LGPL) version 2.0

This is a generic content migration framework, which should help you write
your own content migrations. It has no UI and no value on its own, but
makes it easy to write certain type of content migrations.

This extends the ATContentTypes migration framework to provide three useful 
extensions:

o A CustomQueryWalker can be used to specify a more specific catalog query
    for a walker to use (e.g. which content to actually migrate). This can
    be used with any migrator.

o A BaseInlineMigrator is similar to BaseMigrator, but does not migrate by
    copying the old object to a temporary location, creating a new object and
    applying migration methods. Instead, migration methods are applied in-place.
    This simplifies the code significantly, because attributes, local roles etc.
    does not need to be copied over.

    Note that whereas BaseMigrator works in terms of self.old and self.new as
    the objects being migrated, BaseInlineMigrator only has a single object,
    stored in self.obj. This can be used with any walker.

o An extension of this class called FieldActionMigrator uses the     
    action-based migration framework for Archetypes fields, found in field.py.
    Please refer to that file for full details, but briefly, you specify a list
    of attributes to migrate at the storage level, instructing the migrator
    whether to rename, transform, unset or change the storage for an attribute.

Please see the docstrings in walker.py, migrator.py and field.py for full
details. For examples, see tests/cmtc.py and tests/testATFieldMigration.py.