[Feature request ] Add substraction of unsized vector to insized vector

[Thibault-L]

hiii 😄
I'm using this crate and when you do un unchecked substraction of 2 vector2d
if it go under 0 we got a panic

i don't know if it's a good thing or not I'm still a newbie in rust

thread 'main' panicked at micromath-2.1.0\src\vector\vector2d.rs:151:16:
attempt to subtract with overflow