Initial HDFS Readers and Writers implementation.

Basic implementation of a writer and sequential and random readers that operate with streams on HDFS. These operate on Array[Byte] rather than specific kinds of data, so any data being sent in should already be in serialized form.
Since hadoop-.20 or so append is supported by default. I have never come across a situation where append has not been enabled since like 2010. So I don't see that as a major concern. If it, we can resolve it later.