[WIP] v0.5.0

[bathal1]

Implementing some fixes to issues brought up by issue #43 :

• Support scene files with complicated file structures, e.g. using path and include tags
• Support multiple-camera scenes with references to the children properties (e.g. film, sampler...)

Additional features:

• Support loading meshes in the serialized format.
• Support exporting meshes in the serialized format.

TODO:

• Update version string in __init__.py