overlay_macro 2.0.0

A proc-macro for implementing Overlay, to reinterpret a slice of bytes as a bit/byte packed struct
Documentation 
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A proc-macro for generating a struct which can be overlaid. See the documentation for usage and examples.

## Usage

```rust
#[overlay]
#[derive(Clone, Debug)]
pub struct InquiryCommand {
    #[overlay(byte=0, bits=0..8)]
    pub op_code: u8,

    #[overlay(byte=1)]
    pub enable_vital_product_data: bool,

    #[overlay(byte=2, bits=0..=7)]
    pub page_code: u8,

    #[overlay(bytes=3..=4, bits=0..=7)]
    pub allocation_length: u16,

    ...
}
```

This will create a wrapper struct around an array of bytes, with generated getters and setters for each "field", accessing the bytes/bits at the given offsets.

## Todo

- Support for nested structs
- Support for individual fields larger than `u32` ?
- `compile_error!()` / remove `unwrap` / `expect`
    - And use [trybuild](https://crates.io/crates/trybuild)
    - Emit a fake struct to avoid further errors about it
- Permit missing start/end in byte/bit ranges
- Upgrade to `syn` 2.0
- Don't drop all other attrs on enum members
- Turn off all syn (crate dep) features (except necessary)