Read file in multiple threads and String to Text (#427)

* - Read file in multiple threads if available: 17" -> 15" locally
- Changed String to BytesText with cache: 12" locally

* - Fixed bug
- BytesText to Text
- More checks when reading the file

* - Combining measurements should be thread safe
- More readability changes

calculate_average_japplis.sh

@@ -15,5 +15,5 @@
 #  limitations under the License.
 #
 
-JAVA_OPTS="-Xmx2G"
+JAVA_OPTS=""
 java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_japplis $*