Improve performance of file system traversal.
Add VsixCompress package.
Small code refactorings.
Various code changes

* Optimizations for progress tracking (tick count instead UtcNow, fewer memory allocations)
* Optional optimization path for file name/directory name creation (disabled for now)
* Revamp event handler to capture errors and use standard .net EventArgs classes.
* Various other minor code refactorings.
Merge branch 'master' of https://github.com/chromium/vs-chromium