added Disney BRDF model to API header file.
added Disney BRDF model to API header file.

appleseedhq/appleseed,glebmish/appleseed,Aakash1312/appleseed,appleseedhq/appleseed,gospodnetic/appleseed,docwhite/appleseed,Vertexwahn/appleseed,dictoon/appleseed,glebmish/appleseed,gospodnetic/appleseed,Aakash1312/appleseed,appleseedhq/appleseed,Vertexwahn/appleseed,docwhite/appleseed,docwhite/appleseed,gospodnetic/appleseed,Vertexwahn/appleseed,Aakash1312/appleseed,pjessesco/appleseed,est77/appleseed,Biart95/appleseed,aytekaman/appleseed,docwhite/appleseed,est77/appleseed,gospodnetic/appleseed,Biart95/appleseed,glebmish/appleseed,gospodnetic/appleseed,Aakash1312/appleseed,est77/appleseed,dictoon/appleseed,luisbarrancos/appleseed,pjessesco/appleseed,luisbarrancos/appleseed,pjessesco/appleseed,aiivashchenko/appleseed,aiivashchenko/appleseed,pjessesco/appleseed,Aakash1312/appleseed,appleseedhq/appleseed,aiivashchenko/appleseed,Vertexwahn/appleseed,aytekaman/appleseed,appleseedhq/appleseed,glebmish/appleseed,Biart95/appleseed,luisbarrancos/appleseed,est77/appleseed,aiivashchenko/appleseed,est77/appleseed,Biart95/appleseed,luisbarrancos/appleseed,docwhite/appleseed,pjessesco/appleseed,aytekaman/appleseed,dictoon/appleseed,aytekaman/appleseed,aiivashchenko/appleseed,dictoon/appleseed,luisbarrancos/appleseed,glebmish/appleseed,Biart95/appleseed,Vertexwahn/appleseed,aytekaman/appleseed,dictoon/appleseed