[CSL-789] Add .stack-cache back to Appveyor build cache (#44)
[CSL-789] Add .stack-cache back to Appveyor build cache (#44)

* [CSL-789] Add .stack-cache back to Appveyor build cache

Now it's also branch-namespaced and therefore less susceptible to corruption.

* [CSL-789] Revise comment about Appveyor's caching model

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl