Dodoo

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- better error logging and handling: all exceptions occuring
in scripts under dodoo.env_options are logged and converted
to ClickException so we are sure they are both in the log file
and on the console (handled by click) for the user to see.
The OdooEnvironment context manager does not do additional logging,
leaving that responsibility to the caller.

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- close db connections when releasing OdooEnvironment
- expose dodoo.odoo_bin (odoo or openerp-server depending on Odoo series).
not documented yet, because it should ideally be a full path corresponding
to the installed dodoo.odoo, and I'm not sure how best to detect it yet.

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- minor documentation improvements
- add the possibility to run script without ``--database`` (ie without env,
but with a properly initialized Odoo library such as addons path)
- be more resilient in case we can't obtain a context for the user

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- dodoo now exports the odoo namespace: ``from dodoo import odoo``
is an alias for ``import odoo`` (>9) or ``import openerp as odoo`` (<=9)
- add a ``with_rollback`` option to the ``env_options`` decorator, to control
the presence of the rollback option
- document the ``env_options`` decorator

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- commit in case of success, so users do not need to commit in their
scripts, therefore making scripts easier to compose in larger transactions
- add a --rollback option
- interactive mode forces --rollback

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- clear cache when starting environment (mostly useful for tests)
- simplify and test transaction and exception handling
- when leaving the env, log the exception to be sure it is visible
when using ``--logfile``