Function init 

pub fn init(
    config: &Config,
) -> Result<(TxpoolReadHandle, TxpoolWriteHandle, Arc<ConcreteEnv>), InitError>

Initialize a database & thread-pool, and return a read/write handle to it.

Once the returned handles are Drop::droped, the reader thread-pool and writer thread will exit automatically.

Errors

This will forward the error if crate::open failed.