del = async (key) => {
    if (!await get(key)) { throw new Error(`No document with key '${key}' in the database`) }

    return addOperation({ op: 'DEL', key, value: null })
  }
Deletes a document from the store.
@function
@param {string} key The key of the doc to delete.
@return {string} The hash of the new oplog entry.
@memberof module:Databases.Databases-Documents
@instance