Wrapped SslStream into QueuedStream to prevent concurrent writes.

SslStream does not support concurrent writes. QueuedStream protects the
underlying stream from concurrent writes using a queue.
:lollipop: Added .gitattributes
Revert ":lollipop: Added .gitattributes"

This reverts commit d166de5b1cd73e26066784c649fc890de1e48cd2.
Added unit tests for QueuedStream
Fixed error handling of BeginWrite in QueuedStream

If BeginWrite fails QueuedStream called the wrong callback and did not
schedule the next queued write.
Merge pull request #101 from ugs/master

Wrapped SslStream into QueuedStream to prevent concurrent writes.