Fix a typo

    warning: 1st rule of macro `json_str` is never used
     --> tests/macros/mod.rs:2:5
      |
    2 |     ([]) => {
      |     ^^^^
      |
      = note: `#[warn(unused_macro_rules)]` on by default

    warning: 3rd rule of macro `json_str` is never used
      --> tests/macros/mod.rs:11:5
       |
    11 |     ({}) => {
       |     ^^^^

    error: you are deriving `PartialEq` and can implement `Eq`
      --> tests/test.rs:65:24
       |
    65 | #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
       |                        ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
       |
       = note: `-D clippy::derive-partial-eq-without-eq` implied by `-D clippy::all`
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
      --> tests/test.rs:74:24
       |
    74 | #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
       |                        ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
       --> tests/test.rs:565:25
        |
    565 |     #[derive(Serialize, PartialEq, Debug)]
        |                         ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
        --> tests/test.rs:1278:28
         |
    1278 |     #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
         |                            ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
        --> tests/test.rs:1395:21
         |
    1395 |     #[derive(Debug, PartialEq, Deserialize)]
         |                     ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
        --> tests/test.rs:1415:21
         |
    1415 |     #[derive(Debug, PartialEq, Deserialize)]
         |                     ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
        --> tests/test.rs:1425:21
         |
    1425 |     #[derive(Debug, PartialEq, Deserialize)]
         |                     ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: you are deriving `PartialEq` and can implement `Eq`
        --> tests/test.rs:1627:21
         |
    1627 |     #[derive(Debug, PartialEq, Serialize, Deserialize)]
         |                     ^^^^^^^^^ help: consider deriving `Eq` as well: `PartialEq, Eq`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derive_partial_eq_without_eq

    error: accessing first element with `slice.as_bytes().get(0)`
       --> src/error.rs:441:11
        |
    441 |     match slice.as_bytes().get(0) {
        |           ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `slice.as_bytes().first()`
        |
        = note: `-D clippy::get-first` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#get_first

    error: deref on an immutable reference
       --> src/value/mod.rs:428:45
        |
    428 |             Value::Array(ref array) => Some(&*array),
        |                                             ^^^^^^^
        |
        = note: `-D clippy::borrow-deref-ref` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#borrow_deref_ref
    help: if you would like to reborrow, try removing `&*`
        |
    428 |             Value::Array(ref array) => Some(array),
        |                                             ~~~~~
    help: if you would like to deref, try using `&**`
        |
    428 |             Value::Array(ref array) => Some(&**array),
        |                                             ~~~~~~~~

Eliminate all use of ref keyword

Required by 2021 edition in hashbrown.

    error: failed to download `hashbrown v0.12.1`

    Caused by:
      unable to get packages from source

    Caused by:
      failed to parse manifest at github.com-1ecc6299db9ec823/hashbrown-0.12.1/Cargo.toml

    Caused by:
      failed to parse the `edition` key

    Caused by:
      this version of Cargo is older than the `2021` edition, and only supports `2015` and `2018` editions.

Make Value be From<Option<T>>