It will default to input charset (i.e. the locale charset for now).
Names will be stored internally in that locale charset. Note that input
charset musn't be changed by user. Instead, we can provide an input
charset property to IsoFilesystem implementations.
At this time, nglibisofs is able to output an image!! Note that communication
between writer and read thread is done via a pipe. That will be replaced by a
ring buffer in the near future.