Update and rename java/flatbuffers/FlatBufferBuilder.java to java178/flatbuffers179/FlatBufferBuilder.java

just for fun:
@31 http://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html
Instances of this class are immutable.
@248 Maybe dataStart() should do something else but this is the effect of the method.