TODO

 * INSTALL doc

 * catch EnvironmentError when writing sharefiles and clean up
 * try Duff's device in _addmul1()?
 * memory usage analysis
 * What Every Programmer Should Know About Memory by Ulrich Drepper
 * test handling of filesystem exceptional conditions (tricky)
 * Jerasure
  ** try multiplication without a lookup table? (to save cache pressure)
 * conditional compilation to handle a printf that doesn't understand %Zu
 * try malloc() instead of alloca() (more portable, possibly better for keeping stacks aligned?)

 * announce on lwn, p2p-hackers

 * streaming mode