Gphoto2

1/ Many more functions now allocate and return their outputs, instead of
requiring a new object as a parameter.
2/ Several of the list-like GPhoto2 types can now be iterated over in Python.
3/ Improved memory safety.

1/ Fixed segfault bug with invalid CameraWidget** return values.
2/ Removed need for type-specific gp_widget_get_value_xxx and
gp_widget_set_value_xxx functions.

1/ Changed API of gp_abilities_list_get_abilities and
gp_camera_get_abilities.
2/ Made check_result() much more user-configurable.
3/ Improved memory safety of several functions.

1/ Helper classes now sub-class the corresponding low-level type.
2/ Improved example scripts.

1/ Fixed some bugs in default destructor code introduced in v0.5.0.

1/ Restored '__exit__' methods removed from helper classes in v0.5.0.
2/ Defined some macros to simplify SWIG interface files.