simplify: Increase maximum number of attributes to 32

Generally speaking 16 is plenty, but there are some cases where it's not
quite enough and having some room would be good for experimentation.

src/meshoptimizer.h

@@ -362,7 +362,7 @@ MESHOPTIMIZER_API size_t meshopt_simplify(unsigned int* destination, const unsig
  *
  * vertex_attributes should have attribute_count floats for each vertex
  * attribute_weights should have attribute_count floats in total; the weights determine relative priority of attributes between each other and wrt position. The recommended weight range is [1e-3..1e-1], assuming attribute data is in [0..1] range.
- * attribute_count must be <= 16
+ * attribute_count must be <= 32
  * vertex_lock can be NULL; when it's not NULL, it should have a value for each vertex; 1 denotes vertices that can't be moved
  * TODO target_error/result_error currently use combined distance+attribute error; this may change in the future
  */

src/simplifier.cpp

@@ -521,7 +521,7 @@ static void rescaleAttributes(float* result, const float* vertex_attributes_data
 	}
 }
 
-static const size_t kMaxAttributes = 16;
+static const size_t kMaxAttributes = 32;
 
 struct Quadric
 {