Text Shallow

• character by character, place-holder mode

```rust

use shallow::CharacterShallow;

[test]

fn fillplaceholder() { const TEXT10: &str = "1234567890"; const TEXT21: &str = "12345678901234567890"; const TEXT27: &str = "1234567890123456789012345"; let sb = CharacterShallow::new(21, 5); asserteq!(sb.buildcow(TEXT10), TEXT10); asserteq!(sb.buildcow(TEXT21), "12345678901234567890"); // nothing changed asserteq!(sb.buildcow(TEXT27), "123456789 <...> 12345"); let sb = sb.withshallowtext("..."); // replace shallow text asserteq!(sb.buildcow(TEXT27), "123456789012...12345"); let sb = sb.withendreserved(0); // cancel end reserved asserteq!(sb.buildcow(TEXT27), "1234567890_1234567..."); } ```