Add addHermitCoreRules method to the HasCoreRules class.

[conal]

I needed to generate and add GHC rewrite rules, so I extended the HasCoreRules class

-- | A class of contexts that store GHC rewrite rules.
class HasCoreRules c where
    hermitCoreRules    :: c -> [CoreRule]
    addHermitCoreRules :: [CoreRule] -> c -> c

Some alternatives:

• Split into two classes, like ReadBindings and AddBindings. For consistency, I guess we'd want "ReadCoreRules" and "AddCoreRules", but that'd be a lot of change to client code.
• Add only one rule at a time: addHermitCoreRule :: CoreRule -> c -> c. The [CoreRule] version is perhaps a little more efficient for multiple rules (compared with repeated single additions), while the CoreRule version is more efficient for a single rule. Or maybe not, given GHC's SpecConstr transformation.
• Replace addHermitCoreRules with setHermitCoreRules, since we can build addHermitCoreRules from hermitCoreRules and setHermitCoreRules.

I'm happy to tweak and resubmit.

[conal]

Added some spelling corrections.

[xich]

Just that nit, otherwise happy to merge!

[conal]

Great! I'll make the changes, compile on both 7.10.3 and 8.0.* and re-push.

[conal]

Compiled fine under 7.10.3 and 8.0. Ready to go.

[xich]

Thanks for the patch!