Addresses issue #99: "Mustache spec v1.1.2 compliance"

This is pull request #100 for issue #99: https://github.com/defunkt/pystache/issues/99

Adds test cases and incorporates some clean-ups.

Conflicts:
	pystache/tests/test_context.py
	pystache/tests/test_renderengine.py

  https://github.com/mustache/spec/tree/9b1bc7ad19247e9671304af02078f2ce30132665

Conflicts:
	pystache/context.py
	pystache/tests/test_context.py
	pystache/tests/test_renderengine.py
	tests/common.py

Testing that all elements in a dot-notation path are called (if applicable). Better repr for Attachable test class.

Auto-calling elements in the middle of a dot-notation path (reverts 3c5a6db5)

Conflicts:
	HISTORY.rst

The resolve() function is responsible for the interpolation name
resolution rules described in the Mustache spec.  Also, falsey values
are now coerced to strings using Python's str(), which is more in line
with the spec.