vec*.round(out, a) is asymmetric

[mreinstein]

little known fact: javascript's Math.round(n) is asymmetric; it will round negative numbers towards +∞:

console.log(Math.round(1.5))     // 2    probably we expected this
console.log(Math.round(-1.5))    // -1   what the fack?

because all of our vector modules rely on the built-in Math.round we get this probably unexpected behavior:

const out = vec2.create()
console.log(vec2.round(out, [-1.5, -1.5 ]))  // out === [ -1, -1 ]

This is probably not what most people are expecting. In my own games/simulations I use this module https://www.npmjs.com/package/round-half-up-symmetric to fix this behavior.

Would you be open to a PR that leverages this module wherever we use Math.round(n) ?