Spec updates

[ehildenb]

Fixes: makerdao/mkr-mcd-spec#225

This updates the specs to work with latest KEVM more easily, including:

• Fixes to the write orders in several places (now that KLab generation is sensitive to write order).
• Fixes to some arithmetic expressions that exist in some places.
• Adds an explicit contract address dis-equality Spotter =/= VowVat
• Fixes a markdown formatting error near the Jug_rpow-loop spec which causes KLab to get confused.
• Removes all hardcoded gas expressions (because they are largely obsolete anyway).
• Removes use of #unsigned in favor of direct use of chop.

[WilfredTA]

Write order looks accurate w.r.t. pinned version of DSS

I like added clarity of using chop directly as well