Gocept-cache

================

- Registered clearing the cache with zope.testing.cleanup.

================

- Added memoize_on_attribute to retrieve the memoization cache from the
instance instead of using gocept.cache.method's built-in cache.

==================

- Fixed the bug in `TransactionBoundCache` where the cache was not invalidated
on transaction abort.

==================

- Fixed a bug in `TransactionBoundCache` which yielded an error in the log:
`TypeError: <lambda>() takes exactly 1 argument (2 given)`