Add MonadSAT constraint synonym

[glguy]

See #42

[RyanGlScott]

There are a handful of additional spots where MonadSAT/MonadQSAT could be used:

• https://github.com/ekmett/ersatz/blob/6f3524d0e06c4fe66be45bfe3245729129bb9239/examples/regexp-grid/RegexpGrid/Problem.hs#L62
• https://github.com/ekmett/ersatz/blob/6f3524d0e06c4fe66be45bfe3245729129bb9239/examples/regexp-grid/RegexpGrid/Problem.hs#L70
• https://github.com/ekmett/ersatz/blob/6f3524d0e06c4fe66be45bfe3245729129bb9239/examples/regexp-grid/RegexpGrid/Problem.hs#L115

• In the README.md:

  verify_currying :: (MonadState s m, HasQSAT s) => m ()