state variables should not have syntax restriction and s/be multiformat strings

[michaelcfanning]

The point of state variables is that they display some usable information re: conditions at various points in the code flow. These may be simple values or they may be constraints, assumptions, invariants, etc.

We should accordingly remove the current restriction that these items must conform to a specific language's syntax. Since they are open-ended ('display useful information re: state'), users should have the flexibility moving forward of using markdown to express them.