examples: add primes.v, that shows how to get command line arguments, and use loops and functions

examples/primes.v

@@ -0,0 +1,24 @@
+fn is_prime(n int) bool {
+	if n <= 1 {
+		return false
+	}
+	for i := 2; i * i <= n; i++ {
+		if n % i == 0 {
+			return false
+		}
+	}
+	return true
+}
+
+fn main() {
+	how_many := arguments()[1] or { '10' }.int()
+	mut count := 0
+	mut num := 2
+	for count < how_many {
+		if is_prime(num) {
+			println(num)
+			count++
+		}
+		num++
+	}
+}