Checks if all weights are between 0 and 1.

Switches from GADT syntax to a normal ADT. This is more easily presentable in
writing as it doesn't require additional explanation and is shorter.

Although less explicit about the kind of `f`, it is more clear and easier to
replicate in publications.

This fixes up the haskell examples, so that tangling them to a file results in a
useable powerset implementation.

Creates a new module that exports commonly imported prettyprinter
modules, to cut down on the number of imports each module has to do.

These were originally separated because of some cyclic dependency that
is gone now. So in order to make the module zoo a bit more clear,
merge the two.

(With --no-sanity-checks of course)

This adds --no-sanity-checks to the 'refine' subcommand to pass
DisableSanityChecks to the parser.

Adds a flag to the coalgebra parser that allows individual parsers to
disable all sanity checks on the input.

We previously used the haskell:8.4 docker image, which provides the
latest version of GHC 8.4. Unfortunately, when GHC was upgraded from
8.4.3 to 8.4.4 in the docker image, stack broke because it expected
8.4.3.

To prevent this from happening again, we now use the 8.4.4 docker
image explicitly.

This means that CI is now 8.4.4 instead of 8.4.3.