I'm looking for a boolean interpolation character for `string.format`(as the title says).  

I want something that will work this way: 

```
print(string.format("nil == false: %b",(nil==false))

```

%b is just a placeholder, you'll get an error with that. I'm looking for 'b'. I can't
just do:

```
print("nil == false: " .. (nil==false))

```

because booleans can't be concatenated with strings. I could do: 

```
val=(nil==false)
if val==false then truth="false" else truth="true" end
print("nil==false: ".. truth)

```

But it's too much work.