Changes

4.1.1 (unreleased)

Fix the ExtentFilteredSet to only unindex documents that were previously indexed. This avoids an extra readCurrent call. See issue 12.

Add support for Python 3.7, 3.8 and 3.9.

Note that zopyx.txng3.ext version 4.0.0, the current version at this writing, may or may not build on CPython 3, depending on how your compiler and compiler options treat undefined functions. See this issue.

Also note that both PyPy 3.6 and 3.7 (7.3.4) are known to crash when running the test suite. PyPy2 7.3.4 runs the test suite fine.
When updating indexes in a catalog, first check if the type of each object to be visited implements INoAutoIndex. If it does, we can avoid prematurely activating persistent ghost objects. See issue 8.
Require ZODB 5 in order to use the new prefetch() method.
When adding or updating an index in a catalog, use ZODB's prefetch method to grab chunks of object state data from the database. This can be substantially faster than making requests one at a time. This introduces a new class CatalogPrefetchIterator that may be useful in other circumstances. See issue 7.

Rename TimestampToNormalized64BitIntNormalizer to TimestampTo64BitIntNormalizer for consistency.
Make TimestampTo64BitIntNormalizer subclass TimestampNormalizer for simplicity.
Rename FloatToNormalized64BitIntNormalizer to PersistentFloatTo64BitIntNormalizer for consistency and to reflect its purpose.
Make PersistentFloatTo64BitIntNormalizer subclass FloatTo64BitIntNormalizer.
Add IDeferredCatalog and an implementation in DeferredCatalog to allow creating catalog objects that don't participate in event subscription-based indexing. This replaces IMetadataIndex, which is now an alias for this object. See issue 3.