New compact binary log format: *.buildlog

This release introduces the new binary log format *.buildlog, which also becomes the default. XML is still available. Binary logs can be up to 200x smaller and faster than XML. Depending on which file extension you pass to the StructuredLogger.dll it will write .xml or .buildlog (binary).

The UI can still open and save both formats, but when saving it now defaults to .buildlog.

The binary format is subject to change because the MSBuild Team itself might be coming up with a binary log format. We may switch to using that format in the future.