Higher resolution (bigger) cursors

[9ary]

It looks like hacksaw only comes with a 16x16 cursor, but I use a 32x32 cursor on my desktop (large 4k screen), and the tiny cross is hard to see. It would be a good idea to provide (maybe generate on the fly?) larger cursor sizes.

That said I think it's somewhat useless when guides are enabled, so maybe it should be hidden in that case as well.