Added reset method

Author: ankane

lib/xgboost.rb

@@ -91,7 +91,7 @@ def train(
         evals_result.merge!(cb_container.history)
       end
 
-      bst
+      bst.reset
     end
 
     def cv(

lib/xgboost/booster.rb

@@ -47,6 +47,11 @@ def save_config
       json_string.read_pointer.read_string(length.read_uint64).force_encoding(Encoding::UTF_8)
     end
 
+    def reset
+      check_call FFI.XGBoosterReset(handle)
+      self
+    end
+
     def attr(key)
       ret = ::FFI::MemoryPointer.new(:pointer)
       success = ::FFI::MemoryPointer.new(:int)

lib/xgboost/ffi.rb

@@ -39,6 +39,7 @@ module FFI
     attach_function :XGBoosterUpdateOneIter, %i[pointer int pointer], :int
     attach_function :XGBoosterEvalOneIter, %i[pointer int pointer pointer uint64 pointer], :int
     attach_function :XGBoosterFree, %i[pointer], :int
+    attach_function :XGBoosterReset, %i[pointer], :int
     attach_function :XGBoosterBoostedRounds, %i[pointer pointer], :int
     attach_function :XGBoosterSetParam, %i[pointer string string], :int
     attach_function :XGBoosterGetNumFeature, %i[pointer pointer], :int