examples: add a simplified mini (v)pwgen program

examples/vpwgen.v

@@ -0,0 +1,25 @@
+import os
+import os.cmdline
+import crypto.rand
+import strings
+
+fn main() {
+	blocksize := 256
+	size := cmdline.option(os.args, '-size', '80').int()
+	repeats := cmdline.option(os.args, '-repeats', '4').int()
+	for _ in 0 .. repeats {
+		mut sb := strings.new_builder(blocksize)
+		for {
+			x := rand.read(blocksize)?
+			for c in x {
+				if c >= `0` && c <= `~` {
+					sb.write_b(c)
+				}
+			}
+			if sb.len > size {
+				println(sb.str()[0..size])
+				break
+			}
+		}
+	}
+}