implemented ray depth.
removed experimental surface shaders.
Merge pull request #297 from est77/OSL_merge

OSL merge 6
minor styling fixes.
added UNREACHABLE macro to inform (portably) the compiler that code is unreachable.
renamed some preprocessor symbols.
Changed FOUNDATION_ALIGN to APPLESEED_ALIGN
renamed rules-related elements in project file format.
added a specialization of foundation::from_string() taking a const char*.
tweaked comment.
fixed compilation of devkit sample.
removed skeleton of the new Blender exporter.

this work was picked up by joel d:
https://bitbucket.org/ohsnapitsjoel/render_appleseed
mayaseed no longer ships with appleseed.

mayaseed can be obtained separately here:
https://github.com/appleseedhq/mayaseed
http://mayaseed.net/
demo scenes no longer ship with appleseed.
updated readme.
added source data for test scenes.
no longer force the output color space of the default project to sRGB, use the default color space of the frame (linear RGB).
Added OSL shader param and shader connection classes.
Added OSL shader param and shader connection classes.