This commit removes markupsafe details from the RenderEngine class.

Merry Christmas! :)

Added a unit test and doctest.

We added a case to check that callable return values of __getitem__
are not called.  There is already a test that callable attributes
are called: test_object__attribute_is_callable().

Added a test case for (non-list) "non-false value".

The Renderer class's default loader now inherits the decode_errors
attribute for the instance.

The Renderer class now accepts a loader implementing get()
(e.g. a dictionary or Loader instance) rather than a load_template
function.

Doctests now pass, and they pass running "nosetests --with-doctest".

Apparently, nosetests runs doctests without the doctest.ELLIPSIS
option enabled.  This caused the Modifiers.set() test to fail.

Multiline comments now permitted.  Fix courtesy of fczuardi.

  See https://github.com/defunkt/pystache/issues/33

Ensures that the Renderer class can handle the case of load_template
not returning unicode.