fixed minor issues with R package (#2167)

CMakeLists.txt

@@ -11,7 +11,7 @@ OPTION(USE_OPENMP "Enable OpenMP" ON)
 OPTION(USE_GPU "Enable GPU-accelerated training" OFF)
 OPTION(USE_SWIG "Enable SWIG to generate Java API" OFF)
 OPTION(USE_HDFS "Enable HDFS support (EXPERIMENTAL)" OFF)
-OPTION(USE_R35 "Set to ON if your R version is not smaller than 3.5" OFF)
+OPTION(USE_R35 "Set to ON if your R version is not earlier than 3.5" OFF)
 
 if(APPLE)
     OPTION(APPLE_OUTPUT_DYLIB "Output dylib shared library" OFF)

R-package/demo/categorical_features_prepare.R

@@ -31,7 +31,7 @@ str(bank)
 # For this task, we use lgb.prepare
 # The function transforms the data into a fittable data
 #
-# Classes ‘data.table’ and 'data.frame':	4521 obs. of  17 variables:
+# Classes 'data.table' and 'data.frame':	4521 obs. of  17 variables:
 # $ age      : int  30 33 35 30 59 35 36 39 41 43 ...
 # $ job      : num  11 8 5 5 2 5 7 10 3 8 ...
 # $ marital  : num  2 2 3 2 2 3 2 2 2 2 ...

R-package/src/R_init.c

-
-// Register Dynamic Symbols
-
-#include <R.h>
-#include <Rinternals.h>
-#include <R_ext/Rdynload.h>
-#include "R_init.h"
-
-void R_init_lightgbm(DllInfo* info) {
-    R_registerRoutines(info, NULL, NULL, NULL, NULL);
-    R_useDynamicSymbols(info, TRUE);
-}

R-package/src/R_init.h

-// Register Dynamic Symbols
-#ifndef R_INIT_LIGHTGBM_H
-#define R_INIT_LIGHTGBM_H
-
-void R_init_lightgbm(DllInfo* info);
-
-#endif // R_INIT_LIGHTGBM_H