This extension is a replacement for the subpar, standard Untabify command in Visual Studio. This command replaces all tabs in the selected lines, not just those at the beginning of the line. The correct tab size is maintained, so each line will look exactly as it did before.
This extension is open source. You can find the source here.
-- Version 2: Added support for Visual Studio 2012
-- Version 3: Added support for Visual Studio 2013
-- Version 4: Added support for Visual Studio 2015