update comments. people are more familar with the name 'one-hot encod…

…ing'

core/src/main/java/smile/feature/Nominal2Binary.java

@@ -21,7 +21,8 @@
 import smile.data.NumericAttribute;
 
 /**
- * Nominal variable to binary dummy variables feature generator. Although some
+ * Nominal variable to binary dummy variables feature generator.
+ * This is also called one-hot encoding. Although some
  * method such as decision trees can handle nominal variable directly, other
  * methods generally require nominal variables converted to multiple binary
  * dummy variables to indicate the presence or absence of a characteristic.

core/src/main/java/smile/feature/Nominal2SparseBinary.java

@@ -20,7 +20,8 @@
 import smile.data.NominalAttribute;
 
 /**
- * Nominal variables to sparse binary representation convertor. Here we assume
+ * Nominal variables to sparse binary representation converter.
+ * This is also called one-hot encoding. Here we assume
  * that all variables are nominal attributes and will be converted to binary
  * dummy variables in a compact representation in which only indices of nonzero
  * elements are stored in an integer array. In Maximum Entropy Classifier,