Move math and random files into their respective modules (#198)

* Move math and random files into their respective modules

- Move distanceBetweenPointAndSegment to math module
- Move LCG, randomSeed, and withCustomMathRandom to random module

* Add everything else back

src/random.ts

@@ -0,0 +1,18 @@
+// https://stackoverflow.com/questions/521295/seeding-the-random-number-generator-in-javascript/47593316#47593316
+export const LCG = (seed: number) => () =>
+  ((2 ** 31 - 1) & (seed = Math.imul(48271, seed))) / 2 ** 31;
+
+export function randomSeed() {
+  return Math.floor(Math.random() * 2 ** 31);
+}
+
+// Unfortunately, roughjs doesn't support a seed attribute (https://github.com/pshihn/rough/issues/27).
+// We can achieve the same result by overriding the Math.random function with a
+// pseudo random generator that supports a random seed and swapping it back after.
+export function withCustomMathRandom<T>(seed: number, cb: () => T): T {
+  const random = Math.random;
+  Math.random = LCG(seed);
+  const result = cb();
+  Math.random = random;
+  return result;
+}