Property-cached

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* Overall code and test refactoring, thanks to gsakkis
* Allow the del statement for resetting cached properties with ttl instead of del obj._cache[attr], thanks to gsakkis.
* Uncovered a bug in PyPy, https://bitbucket.org/pypy/pypy/issue/2033/attributeerror-object-attribute-is-read, thanks to gsakkis
* Fixed threaded_cached_property_with_ttl to actually be thread-safe, thanks to gsakkis

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* Regression: As the cache was not always clearing, we've broken out the time to expire feature to its own set of specific tools, thanks to pydanny
* Fixed typo in README, thanks to zoidbergwill

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* Added timed to expire feature to ``cached_property`` decorator.
* **Backwards incompatiblity**: Changed ``del monopoly.boardwalk`` to ``del monopoly['boardwalk']`` in order to support the new TTL feature.

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* Added threading support with new ``threaded_cached_property`` decorator
* Documented cache invalidation
* Updated credits
* Sourced the bottle implementation

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* Fix the dang-blarged py_modules argument.

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* Removed import of package into ``setup.py``