Update mat4 docs to indicate value orientation

Update mat3 docs to clarify value orientation

Corrected bl_info for 2.65 exporter as well [1][2], replaced != and == by "is not" and "is" if comparing with None.

[1] https://projects.blender.org/scm/viewvc.php?view=rev&root=bf-extensions&revision=3086

[2] https://projects.blender.org/scm/viewvc.php?view=rev&root=bf-extensions&revision=4078

Export all cameras in `generate_cameras`, not just the selected one.