Mir-qualia

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Changed
^^^^^^^

- Moved to Python 3.6

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Changed
^^^^^^^

- mir.qualia is now formally specified by ``Qualifier`` tests.

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Changed
^^^^^^^

- BEGIN and END no longer require whitespace between them and the preceding
comment characters.

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Fixed
^^^^^

- Indentation wasn't implemented correctly.

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Changed
^^^^^^^

- Qualified blocks now preserve indentation.

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Fixed
^^^^^

- Unclosed qualified blocks get removed.
- Whitespace is stripped when uncommenting.

Changed
^^^^^^^

- ``IteratorQueue`` and ``CommentPrefix`` are now private, as they are
implementation details.