This reverts commit 01366b63.

This reverts commit 31a59439.

Hoogle v5 `docs` field already contains markup, so we just use the field
content directly.

it's possible to have some content between `<span class=name>` and `<0>`
so separating the expressions to handle this case.

Hoogle v5 uses a different json representation for the data, requires a
new URL and also contains HTML markup inside the json fields.

This commit removes all markup to be able to handle the hoogle responses
using the same structure as with the previous response structure (from
hoogle v4).

update jupyterlab installation procedure in README

Fix haddock generation.

Add ihaskell-graphviz to display graphs.

Requires 'Graphviz' installed.

Update .travis.yml

ihaskell-widgets: Fix more warnings

This file was giving a strange error/warning that had to be disabled.

After investigating this issue (https://ghc.haskell.org/trac/ghc/ticket/15601)
it turns out this was due to an wart in the way type level lists are handled
in GHC. Fortunately a workaround is available allowing the warning to be
re-enabled.

Fix more warnings!

GHC 8.4 and later have the `-Wpartial-fields` warning flag, so add it and
fix the warnings.

Turn on and fix more warnings

ihaskell-widgets: Make it compile with ghc 8.4

Fixing these warnings required changes to the file names of the `MessageHeader`
struct which makes this commit an API change. The version in the cabal file
has been bumped accordingly.