Integration docs

  about non-text transaction meta data.

For backward compatibility, relax the requirements that transaction meta data (user or description) be text

  meta data (user or description) be text

Explicit mode

Fix typo

Add SQLAlchemy and repoze.sendmail to integration documents

Document why newTransaction is only called by begin.

We have no C extensions, and therefore do not need to exclude their
derived files in 'MANIFEST.in'.

extended-info -> extension

I'll make the transaction release and then I'll push an update to the ZODB PR that works with the change.

renamed to ``extension``.

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