Function grin_chain::txhashset::header_extending

pub fn header_extending<'a, F, T>(
    handle: &'a mut PMMRHandle<BlockHeader>, 
    batch: &'a mut Batch, 
    inner: F
) -> Result<T, Error> where
    F: FnOnce(&mut HeaderExtension, &Batch) -> Result<T, Error>, 

Start a new header MMR unit of work. This MMR can be extended individually beyond the other (output, rangeproof and kernel) MMRs to allow headers to be validated before we receive the full block data.