Merge pull request #17 from jasperges/master

Small fixes based on my tests on OSX
Fixed error with deformation mesh objects being written to .appleseed file.
Didn't need preview in world tab, since it's not related to Blender's world settings.
Added support for experimental features:
-Disney BRDF / Disney BRDF node
-Diaphragm map
-Hair curve rendering (has to be enabled in render settings.  Need to remove some old settings from ui / properties until they're added to appleseed curve support)
Minor changes to particle system export.
Fixed specular btdf IOR assignments.
Fixed mesh_writer.py to work when not using compiled modules
updated README.md
updated README.md
Merge branch 'master' of https://github.com/appleseedhq/blenderseed

Conflicts:
	README.md
Stupid Git!
Fixed typo.
Merge pull request #19 from est77/est

Fixed typo.
Hide hair rendering properties from UI