Choose your own aesthetic

While working on Prusa3/box_frame models I got in argument with Jo, as he says that rouded corners are ugly, but I like them. The main reason is that parts with rounded corners are less prone to breaking off the heatbed while printing. Second reason is that that rounded parts are less likely to have waves on smooth walls, which are mainly result of sudden direction (and thus speed) change. To keep all sides happy, I introduced use_fillets config variable. You can see effects on the parts:

Default (use_fillets=1):

For those that like boxes (use_fillets=0):

But yes, there is more (use_fillets=2):

The possibilities are sorted in the order of probablility of working well out-of-the-box, I have not tested the last variant at all yet.