Spec cleanups

 - Add a better intro
 - Qualify metavariable use
 - Add a SR instruction
 - Renumber SLR and SAR to fit in SR
Synchronize the single cycle VMs

 - Refactor out common state operations into isa
 - Ensure that the same printing behavior is provided in writeback
 - Refactor for style
Refactor single cycles for ISA coverage

Implement all ISA control and data instructions save for the arithmetic
shift operators in both the bytecode and single cycle machines.