Updated .gitignore
Update .gitignore
Framerate Limiting

Added a framerate limit of 60 FPS
Added User-Defined Screen Size
Fixed mistake with Width/Height
Added User-Defined Centre Particle's Mass

"I’ve always thought that one of the the great things about physics is
that you can add more digits to any number and see what happens and
nobody can stop you."
-- Randall Monroe
Added User-Defined Velocity, Tidied up.

YAY - CRAPPY ASCII ART!!!

And also I added a couple of features.
I think we have a merge problem.

Hope this will fix it.