Add a format function to vector and matrix structs

[hordurj]

It would be convenient to include a format function in Vec and Mat structs (and other similar types) for easy printing of these types (std.debug.print, allocPrint, etc).

Default for Vec2 is:
math.vec.Vec(2,f32){ .v = { 1e0, 2e0 } }

A more compact Vec2 output:
[1.0 2.1]
or
1.0, 2.1
or
1.0 2.1

Mat2x2:
[[1.0, 0.0], [0.0, 1.0]]
or
[1.0 0.0] [0.0, 1.0]

Or something along these lines.

https://ziglang.org/documentation/master/std/#std.fmt.Formatter