Macro impl_to_hex_from_lower_hex

macro_rules! impl_to_hex_from_lower_hex {
    ($t:ident, $hex_len_fn:expr) => { ... };
}

Adds an implementation of pub fn to_hex(&self) -> String if alloc feature is enabled.

The added function allocates a String then calls through to core::fmt::LowerHex.

Note: Calling this macro assumes that the calling crate has an alloc feature that also activates the alloc crate. Calling this macro without the alloc feature enabled is a no-op.