Zeo-connector

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- Pinned older version of ZEO.

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- Cleanup of metadata files.

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- Added ``retry_and_reset`` decorator for all internal dict-methods calls.
- Project key is now optional, so this object may be used to access the root of the database.
- Property ``ASYNCORE_RUNNING`` renamed to ``_ASYNCORE_RUNNING``.
- Implemented ``.pack()``.
- Added ``transaction_manager``.
- Added ``examples/database_handler.py`` and tests.
- Added wraps(fn) to decorators.
- Added requirement for zope.interface.
- Attempt to solve https://github.com/WebArchivCZ/WA-KAT/issues/86

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- Environment generator and other shared parts moved to https://github.com/Bystroushaak/zeo_connector_defaults
- README.rst improved, added more documentation and additional sections.

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- Small bugfix.
- Removed unused files.

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- Switched to complete randomly generated ZEO environment (random name in /tmp, and random ports for ZEO server process).