Add sundown submodule
Autonome build project

Add sundown.pri and make qarkdown.pro use it if sundown folder is found.
This make possible to have a buildable project without the sundown lib isntalled on the system.
Ignore QtCreator pro.user files
Add better plain text editor which support indent / unindent
Add some formatting support in toolbar
Show maximized by default
Merge pull request #4 from pasnox/master

Enhancements