Added support for 'import_', 'import_stl', and 'import_dxf', which all resolve to the OpenSCAD statement 'import'
Merge branch 'master' into develop

* master:
  Start adding sphinx documentation
  Fix tests to not fail if run from the parent directory
  Add missing png requirement
  Expand test cases to output a diff on assertEqual failing instead of the strings which are hard to understand.
  Fix issues with install_data missing from the sdist package.
  Added License link to TOC
  Add license information to the README
  fixes gh-18   scad_render_to_file() now can be called from the terminal
All tests now pass in Python 2.7.5 and Python 3.4.1 (if a Python 3-compatible Pyeuclid is installed.)
Changed README.md to reflect that SolidPython can be installed using pip.