merged version of
 BufferedOutputStream and DataOutputStream, wrt SystemDS requirements.
 
 Micro-benchmarks showed a 25% performance improvement for local write binary block
 due to the following advantages: 
 - 1) unsynchronized buffered output stream (not required in SystemDS since single writer)
 - 2) single output buffer (avoid two-level buffers of individual streams)
 - 3) specific support for writing double arrays in a blockwise fashion</div>
</li>
</ul>
</div>
<div class="summary">
<ul class="blockL