Implement most semi-finished functionalities

Implement most semi-finished functionalities

Summary of new functionalities:

* Add support for 4 different xseg operations (read, write, info,
  delete).
* Add support for random I/O patterns with a fast Galois LFSR.
* Add insanity levels in timers, which allow the user to exclude obscure
  timers from the benchmark (or explicitly allow them)
* Generate target names based on seeds given by the user or produced by
  the benchmark (useful for reproducibility of benchmark)