Add Dockerfiles for building and running C,Coq and Haskell projects

[imaginator]

I've created the following files:

Dockerfile.c
Dockerfile.haskell
Dockerfile.coq

Builds are now self contained and drops the user into either a ghci or coq prompt. Ideally we could publish these containers to Dockerhub which would make it easier for experimenting [without waiting for long builds].

The README.md needs a bit of a rework too, but that's another project.

[apoelstra]

I will go ahead and run my local CI on this, though I checked that no existing source files are changed. I don't have docker installed on any of my systems and I'm not really familiar with the syntax or what these containers are supposed to do.

[imaginator]

@apoelstra their use is documented in the README.md file. For example the building and running the Coq version should give a coqtop prompt with everything built. Likewise, the haskell image presents a GHCi console with correct Simplicity modules loaded. (https://github.com/BlockstreamResearch/simplicity/pull/309/commits/6892b08658a9ddfca7a47f11372ce0e00c7d9a1b)

My thinking behind these is that it makes an easy way to write tutorials and, like with Nix images, present users with all the dependencies they need to get experimenting with Simplicity quickly.