Parses hexadecimal float literals.
There are two functions `parse_hexf32` and `parse_hexf64` provided for each type.
```rust
use hexf_parse::*;
assert_eq!(parse_hexf32("0x1.99999ap-4", false), Ok(0.1f32));
assert_eq!(parse_hexf64("0x1.999999999999ap-4", false), Ok(0.1f64));
```
An additional `bool` parameter can be set to true if you want to allow underscores.
```rust
use hexf_parse::*;
assert!(parse_hexf64("0x0.1_7p8", false).is_err());
assert_eq!(parse_hexf64("0x0.1_7p8", true), Ok(23.0f64));
```
The error is reported via an opaque `ParseHexfError` type.