v0.0.1

This is the first release since this was forked from https://github.com/kdomanski/iso9660

Main changes:

• Allow change of any field of the primary volume descriptor by exposing it (see example in README for setting volume name, for example)
• Remove use of a staging directory by storing information in memory instead
• Add AddLocalFile to add a file without having to load it into memory or keep a file descriptor open while preparing the disk
• Expose a AddBoot method in ImageWriter to allow addition of a boot volume descriptor in the newly created image
• Change the WriteTo() parameter to use a io.Writer instead of io.WriterAt so image can be streamed (via http for example)

Feedback is welcome.