Pyinvoke

- :feature:`109` Add a ``default`` kwarg to
`invoke.collection.Collection.add_task` allowing per-collection control over
default tasks.
- :feature:`108` Update `invoke.collection.Collection.from_module` to accept
useful shorthand arguments for tweaking the `invoke.collection.Collection`
objects it creates (e.g. name, configuration.)
- :feature:`107` Update configuration merging behavior for more flexible reuse
of imported task modules, such as parameterizing multiple copies of a module
within a task tree.

- :bug:`86 major` Task arguments named with an underscore broke the help feature;
this is now fixed. Thanks to Stéphane Klein for the catch.
- :feature:`89` Implemented configuration for distributed task modules: can set
config options in `invoke.collection.Collection` objects and they are made
available to contextualized tasks.

- :bug:`81` Fall back to sane defaults for PTY sizes when autodetection gives
insane results. Thanks to ``akitada`` for the patch.
- :bug:`83` Fix a bug preventing underscored keyword arguments from working
correctly as CLI flags (e.g. ``mytask --my-arg`` would not map back correctly
to ``mytask(my_arg=...)``.) Credit: ``akitada``.

- :feature:`57` Optional-value flags added - e.g. ``--foo`` tells the parser to
set the ``foo`` option value to True; ``--foo myval`` sets the value to
"myval". The built-in ``--help`` option now leverages this feature for
per-task help (e.g. ``--help`` displays global help, ``--help mytask``
displays help for ``mytask`` only.)
- :bug:`55 major` A bug in our vendored copy of ``pexpect`` clashed with a
Python 2->3 change in import behavior to prevent Invoke from running on
Python 3 unless the ``six`` module was installed in one's environment. This
was fixed - our vendored ``pexpect`` now always loads its sibling vendored
``six`` correctly.