a simple interface for querying stdin
This assumes that you have called `atty::is(Stream::Stdio)` before calling `qstdin::is(Stdin::*)`
```console
$ cargo add qstdin
```
```console
$ cargo run --example qstdin
input? true
file? false
directory? false
```
```console
$ cargo run --example qstdin < Cargo.toml
input? false
file? true
directory? false
```
```console
$ cargo run --example qstdin < src
input? false
file? false
directory? true
```