message: Update data library documentation
  Update links to MDL declarations and implementations.
  Remove references to the legacy OSL reference library (now superseded by genosl).
diff: @@ -18,12 +18,10 @@ This folder contains the standard data libraries for MaterialX, providing declar
  - [stdlib_genosl_cm_impl.mtlx](stdlib/genosl/stdlib_genosl_cm_impl.mtlx) : Minimal set of "default" color management implementations.
  - [stdlib_genosl_unit_impl.mtlx](stdlib/genosl/stdlib_genosl_unit_impl.mtlx) : Real world unit support implementations.
  - OSL implementation files.
  - - [osl](stdlib/osl): OSL reference implementations.
  - - These are the original OSL reference implementations from MaterialX v1.35, and will be replaced with generated OSL code in the future.
  - [genmdl](stdlib/genmdl): MDL language support.
  - - [stdlib_genmdl_impl.mtlx](stdlib/genosl/stdlib_genmdl_impl.mtlx) : Mapping from declarations to implementations.
  - - [stdlib_genmdl_cm_impl.mtlx](stdlib/genosl/stdlib_genmdl_cm_impl.mtlx) : Minimal set of "default" color management implementations.
  - - [stdlib_genmdl_unit_impl.mtlx](stdlib/genosl/stdlib_genmdl_unit_impl.mtlx) : Real world unit support implementations.
  + - [stdlib_genmdl_impl.mtlx](stdlib/genmdl/stdlib_genmdl_impl.mtlx) : Mapping from declarations to implementations.
  + - [stdlib_genmdl_cm_impl.mtlx](stdlib/genmdl/stdlib_genmdl_cm_impl.mtlx) : Minimal set of "default" color management implementations.
  + - [stdlib_genmdl_unit_impl.mtlx](stdlib/genmdl/stdlib_genmdl_unit_impl.mtlx) : Real world unit support implementations.
  ## Physically Based Shading Library
  - [pbrlib](pbrlib)
  @@ -38,7 +36,7 @@ This folder contains the standard data libraries for MaterialX, providing declar
  - [pbrlib_genosl_impl.mtlx](pbrlib/genosl/pbrlib_genosl_impl.mtlx) : Mapping from declarations to implementations.
  - OSL implementation files.
  - [genmdl](pbrlib/genmdl) : MDL language support
  - - [pbrlib_genmdl_impl.mtlx](pbrlib/genosl/pbrlib_genmdl_impl.mtlx) : Mapping from declarations to implementations.
  + - [pbrlib_genmdl_impl.mtlx](pbrlib/genmdl/pbrlib_genmdl_impl.mtlx) : Mapping from declarations to implementations.
  - Note: MDL implementation files are in a "package" folder found under [source/MaterialXGenMdl/mdl/materialx](../source/MaterialXGenMdl/mdl/materialx)
  ## BxDF Graph Library
  