Basic implementation of HDFS WAL.
Make most methods in writer and reader thread-safe.
Add a method to close files
Add preconditions checks to ensure that the writer or reader has not closed the stream before doing any operations
Making FileSegment a case class
Making all HDFS Wal classes private to streaming
Make close methods synchronized, to ensure close does not get called in the middle of a write
Make the Sequential reader an Iterator. Rename all classes. Mark all assertOpen methods private.
Make all variables private
Minor changes to definitions of methods
Merge pull request #12 from harishreedharan/hdfs-wal

Initial HDFS Readers and Writers implementation.