A Directory is a flat list of files. Files may be written once, when they
/// are created. Once a file is created it may only be opened for read, or
/// deleted. Random access is permitted both when reading and writing.
///
/// Java's i/o APIs not used directly, but rather all i/o is
/// through this API. This permits things such as:
/// - implementation of RAM-based indices;
///
- implementation indices stored in a database, via JDBC;
///
- implementation of an index as a single file;
///
///
///
///