Add support for XSIM productions; expand tests to cover more file types

Closes #72 (closed)

Features:

• Add support for XSIM productions
• Expand reference tests to cover more file types

Bugfixes:

• Input of Boole step is now matched to output of Gauss step. Added validation check to ensure consistency of input/output between all consecutive steps
• Reference tests now sensitive to different number of steps. Would previously give false-positive if all steps were the same and one had additional steps that the other didn't