Reset and re-run the drawing process

[gege2b]

Hi there
First, thank for this pretty cool piece of software, I really love the results

For my use, I Added the ability to reset the program and run another drawing in a row. Maybe someone will find this feature interesting, hence the pull request.

This avoid the necessity to close/reopen the program to draw another picture, just press 'R', select another file and go on !

Note : there is still a little bug I didn't success to catch : just after reseting, sometimes, the drawing didn't start, we need to press a key on the keyboard (or pan the drawing aera) to start the process
My guess is it has something related to file selection routine but I still need to dig deeper.

feel free to comment

[Scott-Cooper]

Hey gege2b, I really like this code and will be merging after I find that little bug.