A small macro for flattening a map type with regex machting keys.
```rust
struct RouterStatus {
id: u32,
wifistatus: bool,
#[flatregex(regex = r"lanportstatus_\d+")]
lanports: std::collections::HashMap
fn jsontest() { let raw = r#"{ "id": 1, "wifistatus": true, "lanportstatus0": "UP", "lanportstatus1": "UP", "lanportstatus_2": "DOWN", "lanportspeed": "100" }"#;
let router_status: RouterStatus = serde_json::from_str(raw).unwrap();
assert_eq!(router_status.lanports.len(),3)
} ```
The collection for flattening must be a serde-map type and implement Extend<(K,V)> + Default
. The key can be anything that implements AsRef<str>