The mt19937 from seehuhn

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Go's PRNG appears to be a LFG

Though you would like to know http://willyschultz.com/2017/06/30/cracking-golang-prng.html

The usages in README.rst and example.go are not goroutine-safe

README.rst and example.go says

rng := rand.New(mt19937.New())
rng.Seed(time.Now().UnixNano())

But this usage is not safe for concurrent use by multiple goroutines.

In fact, the following code sometimes panics:

package main

import (
	"math/rand"
	"sync"
	"time"

	"github.com/seehuhn/mt19937"
)

func main() {
	rng := rand.New(mt19937.New())
	rng.Seed(time.Now().UnixNano())

	num := 1000000

	var wg sync.WaitGroup
	start := make(chan struct{})
	for i := 0; i < 2; i++ {
		wg.Add(1)
		go func() {
			<-start
			for i := 0; i < num; i++ {
				_ = rng.Int()
			}
			wg.Done()
		}()
	}
	close(start)
	wg.Wait()
}

❯ go run main.go
panic: runtime error: index out of range [312] with length 312

goroutine 5 [running]:
github.com/seehuhn/mt19937.(*MT19937).Int63(0xc00000c060, 0x465861f52497b634)
	/Users/skaji/src/github.com/seehuhn/mt19937/mt19937.go:156 +0x23b
math/rand.(*Rand).Int63(...)
	/Users/skaji/env/go/src/math/rand/rand.go:85
math/rand.(*Rand).Int(...)
	/Users/skaji/env/go/src/math/rand/rand.go:103
main.main.func1(0xc000072060, 0xf4240, 0xc000078090, 0xc00001a0e0)
	/Users/skaji/try/20191103/main.go:24 +0x55
created by main.main
	/Users/skaji/try/20191103/main.go:21 +0x221
exit status 2

In math/rand, sources are wrapped by lockedSource.
https://golang.org/src/math/rand/rand.go#L288
I think README.md and example.go should suggest such usage too.