configurable
 - file store
   - type
   - name
 - is read only
 - path characters to reject
 - case insensitive comparison (normalization)
 - FileTypeDetector
 - Paths.get lazily create file system?
 - fill with random data #position() past end
 - size() of directory
 - configure range of setTimes (past 2038)
 - security manager restrictions
 - relative path with only one element
