In-memory compressed String

If your application keeps many long strings in RAM, you can reduce its memory usage by compressing the strings.

Optionally, if with_serde feature is enabled, it can also be used to serialize and deserialize strings in binary formats in an already-compressed form.

```rust use compressed_string::ComprString;

let raw = "It uses the deflate algorithm, which has a small header overhead, \ so it's suitable even for short-ish strings";

let compr = ComprString::new(raw);

asserteq!(109, raw.len()); asserteq!(84, compr.compressed_len());

println!("{}", compr); let string = compr.to_string(); ```