CurInstallProgressChanged event by TLama, see #51
Remove TInstallStep steps which don't actually cause any progress update.

Thinking about removing it all together, not convinced it's very usefull. Also don't like the name.
Updated help and demo.
Removed TInstallStep. Improved parameter names in example and help as suggested by TLama. Updated whatsnew. #51.
Merge branch 'CurInstallProgressChanged'