Limit strength factor to 1,000

Fixes Nocte-#49

Version bump to 0.2.4

See pull request Nocte-#39

Bump to 0.2.3

Renamed COPYING to LICENSE.md

Change to MIT/Expat license

Fixes Nocte-#20

Nicer example

Make on_resolve and on_variable_change less chatty

Fixes Nocte-#13