coercing to a valid type or defaulting to None.

Added GroundOverlay from string test case that uses a sample kml from Google reference documentation.

* Attempt to solve issues with Python 2.6 unittesting when using the:
    with self.assertRaises(...): ...
  By specifying "as context" on the with statement

Finished implementation of the GroundOverlay class. All that is still needed is the <gx:latLonQuad> tag.

* Implemented the altitude property and etree_element() functionality.

Add support for <address> and <phoneNumber> tags.

Handle case where Feature booleans are 'true' or 'false' during parsing, No need to preserve the original values if they are in violation of the specification, we may need to adjust isOpen and visibility so it defaults to the specifications default values

parsing from string

Fixed issue (line length) with kml.py that kept pep8 test from passing.

Fixed bug in which documents inside directories were ignored.

Conflicts:
	fastkml/kml.py

Pep8

following style checkers:
* pep8 (version 1.5.7)
* pyflakes (version 0.7.3)

Fix typo, add pip requirements file, test for kml.KML.from_string when not a kml string
Thanks 8-)

This form is compatible with Python 2.6.

Fixes the failures found with Travis builds [53, 54]