Flush buffer for every benchmark data

I'm doing this, hoping that it prevents problems memory leaks in the
when writing the feature vectors to a file.

core/src/main/kotlin/se/lth/cs/SyntheticBenchmarkDataPrinter.kt

@@ -39,6 +39,7 @@ abstract class SyntheticBenchmarkDataPrinter(out : Writer,
         for (syntheticBenchmark in syntheticBenchmarks) {
             System.out.println("Printing benchmark: %s".format(syntheticBenchmark.benchmarkIdentifier))
             printBenchmarkRows(syntheticBenchmark)
+            printer.flush()
         }
 
         printer.close()

core/src/main/kotlin/se/lth/cs/commandline/PapiCommandLine.kt

@@ -13,10 +13,7 @@ import se.lth.cs.papicounters.PAPICounter
 import se.lth.cs.papicounters.PapiTracerRunner
 import se.lth.cs.util.brainyFeatures
 import se.lth.cs.util.normalize
-import java.io.File
-import java.io.FileReader
-import java.io.FileWriter
-import java.io.Reader
+import java.io.*
 import java.util.stream.Collectors
 import java.util.stream.Stream
 import kotlin.system.exitProcess