win/msi: separate features for ETW and perfctr support
win/msi: make 'add to path' a separate feature
win/msi: refactor 'node.js runtime' feature

* This feature now includes the start menu items.
* 'nodejsvars.bat' was renamed to 'nodevars.bat'.
* Improved feature description.
win/msi: clean up the 'documentation shortcuts' feature
win/msi: update 'install finished' message
win/msi: don't include architecture in start menu group name
win/msi: miscellaneous style cleanups