align expressed RNA sequences on a DNA template

 The SIBsim4 project is based on sim4, which is a program designed to align
 an expressed DNA sequence with a genomic sequence, allowing for introns.
 SIBsim4 is a fairly extensive rewrite of the original code with the following
 goals:
  * speed improvement;
  * allow large, chromosome scale, DNA sequences to be used;
  * provide more detailed output about splice types;
  * provide more detailed output about polyA sites;
  * misc code cleanups and fixes.