* thread
* index tarballs
	* just a list of files?
	* sorted?
	* ranges?
	* reading tars
		* libarchive?
		* copyfile/multi-header aware

* sane, safe errors
	* signal safe?
	* return values, don't die
	* don't leak
	* malloc errors?
* command-line options
* autoconf
* optimized settings
	* scale threads/memory to physical RAM
	* scale threads to CPUs (gcd?)
* init/cleanup
* keep the same stream for multiple blocks?
	* even use the same buffers?
	* don't write block header until we're writing to file?
* support multiple streams?

* append to tarballs without decompressing?