…nd-bools

Add literal 'null', 'true' and 'false' consts to `RawValue` struct.

…ctions

Move RawValue associated constants into same impl block as public functions

    warning: operator precedence can trip the unwary
       --> src/read.rs:963:18
        |
    963 |         let n = (((n1 - 0xD800) as u32) << 10 | (n2 - 0xDC00) as u32) + 0x1_0000;
        |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(((n1 - 0xD800) as u32) << 10) | (n2 - 0xDC00) as u32`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
        = note: `-W clippy::precedence` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::precedence)]`

    warning: operator precedence can trip the unwary
       --> src/read.rs:991:28
        |
    991 |                 ptr.write((n >> 6 & 0b0001_1111) as u8 | 0b1100_0000);
        |                            ^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(n >> 6) & 0b0001_1111`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

    warning: operator precedence can trip the unwary
       --> src/read.rs:995:28
        |
    995 |                 ptr.write((n >> 12 & 0b0000_1111) as u8 | 0b1110_0000);
        |                            ^^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(n >> 12) & 0b0000_1111`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

    warning: operator precedence can trip the unwary
       --> src/read.rs:996:35
        |
    996 |                 ptr.add(1).write((n >> 6 & 0b0011_1111) as u8 | 0b1000_0000);
        |                                   ^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(n >> 6) & 0b0011_1111`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

    warning: operator precedence can trip the unwary
        --> src/read.rs:1000:28
         |
    1000 |                 ptr.write((n >> 18 & 0b0000_0111) as u8 | 0b1111_0000);
         |                            ^^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(n >> 18) & 0b0000_0111`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

    warning: operator precedence can trip the unwary
        --> src/read.rs:1002:29
         |
    1002 |                     .write((n >> 12 & 0b0011_1111) as u8 | 0b1000_0000);
         |                             ^^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(n >> 12) & 0b0011_1111`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

    warning: operator precedence can trip the unwary
        --> src/read.rs:1003:35
         |
    1003 |                 ptr.add(2).write((n >> 6 & 0b0011_1111) as u8 | 0b1000_0000);
         |                                   ^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(n >> 6) & 0b0011_1111`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

Signed-off-by: tison <wander4096@gmail.com>

Add Map::into_values method