Blog Post Rewrite - Callback Signal Chains

[Ron Tarrant via Digitalmars-d-learn]

While doing screenshots for the gtkDcoding blog (See? I'm working 
on it.) I discovered something cool about signal callback chains 
in GtkD. So, I ended up rewriting the code and the blog post to 
include this coolness.

You can read it here: 
http://gtkdcoding.com/2019/02/19/0011-callback-chains.html