Merge branch 'release/1.0.1' into develop
Removed superfluous pypy distribution environments.
Attributes redefined in a subclass as a non-Attribute are correctly excluded.  Fixes #5.
Now preserves order, delays sorting attributes until later.  Fixes #1.
Added `__fixup__` (inclusion) and `__attributed__` (definition) callbacks.  Fixes #7.
Added ticket references to the tests.
Added tuple sizing utility and related tests.

This will be useful in a short while…
Added third party package examples.

This is mostly to account for a reasonable level of compatibility with
these packages, and to allow me to identify a level of “completeness”
of the marrow.schema API.
Extracted common compatibility code.
Added simple boolean helpers and added missing builtins.
Removal of dead code.
Validation failure exception class, with tests.
Added 1.0.2 version history.
Bumped version number.
Merge branch 'release/1.0.2'