Add API documentation using Doxygen
Fix build, move worker code to qpython_worker
Disable some unused documentation features
Add some instructions how to build for BB10
Documentation fix
qpython_priv: Avoid crash when no QPython object was ever instanced

When importing "io.thp.pyotherside" in a QML file, but no Python {}
object is created during runtime, PyOtherSide would crash at exit.
Add support for Python-based image providers. Fixes #1
Image provider: Support returning encoded image data

This allows the additional use case of reading e.g. PNG tiles from a
database and passing them to Qt without decoding first (see issue #1).
Example using matplotlib + numpy