Merge branch 'master' into help-output

Conflicts:
	invoke/cli.py
	invoke/parser/__init__.py
	tests/cli.py
Clarify docstrings
Fix up non-function callable collection.add_task test
Fix other failing test.

Now the only failing test is the one we expect.
Specifically, the format of help output.
Formatting/comment tweak
Port tweaked copy of Fabric's utils._pty_size
Update expected --help output:

* Add missing version, list options
* Line things up into columns-ish
Further comment/expected-output tweaks to --help
Comment updates in impl
Change help_for in prep for columnification
s/help_lines/help_tuples