Transform managed in a class based context manager.
Make context.managed function as decorator as well.
Change assert statements to methods (Geron style).
Remove commit_on_success() doc.
Add managed() as decorator docs.
Adding f() missing calls
Change Alchemy dependency to a broader range.
Merge pull request #9 from etandel/develop

Change Alchemy dependency to a broader range.
Version bump: 0.4
Merge branch 'release/0.4'