spec out dataset splitter
docs
Add failing test for splitting data
refactor test
add createMap + test
add testSplitMap
testSplitMap passes
test fails because reader at end after generating map
workaround issue with reading stream twice.  tests pass
add code to read datafile gzip stream, untested.
add piped reader/writer, seems to be working
trying to use io.pipe .. total fail
stores everything a buffer, but at least successfully saves to cbfs

note: the tar file is messed up in terms of permissions and missing folders.
Propagate tar header correctly, to preserve username etc
Fix issue with io.pipe not working since underlying writers not closed
Code cleanup and docs