Remove dependency on Stack

[atomb]

This removes the dependency on Stack, in several ways:

• Removes the use of Stack in the test suite.
• Updates build.sh to use cabal build.
• Updates coverage.sh to use cabal build --enable-coverage.
• Updates the README to describe how to build with cabal.
• Removes Stack configuration files.

It also fixes a broken test along the way.

[brianhuffman]

I still use stack for local builds (due to its --copy-bins functionality, which I like, and which cabal doesn't have). What does removing the stack configuration files mean for me? Having up-to-date stack.yaml files in the repo is pretty convenient, although I guess if the ones in the repo ever get broken, they become more of a hindrance... and nothing in CI ensures that they don't get broken.

I guess I can probably just maintain my own stack configuration files independently, as long as I want to keep using them. This will probably work fine most of the time; doing old builds (e.g. during bisection) might get a bit trickier if they need different stack configurations, but I guess the stack.yaml files generally don't need to change very often.

[atomb]

Thanks for mentioning that, @brianhuffman. My main goal here was to make the central scripts independent of Stack, since we're mostly not using it in CI anymore, but the fact that it's used in the test script could potentially lead to some things being built twice. That doesn't necessarily mean we need to take out the configuration files, though, in case someone wants to use it. I'd be happy to revert that part of the PR.