Open/New/Save functions

[liquid]

I would suggest to change a little bit behaviour of Open/New/Save to be as common as with other software working on documents.

• If you exit program with unmodified file then no warning;
  
• If you save file manually then clear modified flag;
  
• If you press New and current file is modified then warning and possibly save
  
• If you press New and current file is unmodified then no warning
  

If I'm right the only issued warning is when you exit program regardless whether file is modified or not.

[Liviu Lalescu]

There is also warning/confirmation if you want a new file.

I'll think of your suggestion and add it in the TODO.