v0.5.0

Breaking changes

1. Widget creation now use method chain to set various properties.
   For example:
   Old style widget creation

giu.InputTextMultiline("Text area", &content, 300, 100, 0, nil)
giu.Button("Click Me", func() { fmt.Println("Clicked") })

New style widget creation

giu.InputTextMultiline("Text area", &content).Size(300, 100)
giu.Button("Click Me").OnClick(func() {...})

All xxxV methods are removed.

With method chain, giu becomes more flexible to add properties and events to any widget in future.

2. Rename MasterWindow.Main(...) to MasterWindow.Run(...).