Session.begin() returns a context manager

[Felix Mühlbauer]

In the example code of autocommit the return value of Session.begin() is used as a context manager. This is not described in the docs for Session.begin()

[Mike Bayer]

• add complete parameter /return value docs to session.begin() / session.begin_nested(). Fixes #3993

Change-Id: If485d77b364c34d94061d2f48efbde3f8a8adec9

→ <<cset 4c6917e1d68a>>

[Mike Bayer]

• add complete parameter /return value docs to session.begin() / session.begin_nested(). Fixes #3993

Change-Id: If485d77b364c34d94061d2f48efbde3f8a8adec9 (cherry picked from commit 4c6917e1d68a8baab7efe10e9ce5e5c8187f65ca)

→ <<cset c050a449def1>>

[Mike Bayer]

• add complete parameter /return value docs to session.begin() / session.begin_nested(). Fixes #3993

Change-Id: If485d77b364c34d94061d2f48efbde3f8a8adec9 (cherry picked from commit 4c6917e1d68a8baab7efe10e9ce5e5c8187f65ca)

→ <<cset 96cfda6f640e>>