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.