* FromJSON class

Aeson style FromJSON class with Parsec based json parser.

* doc-index.json file for multiple packages

When creating haddock summary page for multiple packages render
doc-index.json file using contents of all found 'doc-index.json' files.

* Render doc-index.json

When rendering html, render doc-index.json file independently of
maybe_index_url option.  doc-index.json file is useful now even if
maybe_index_url is not `Nothing`.

* base url option

New `Flag_BaseURL` which configures from where static files are loaded
(--base-url).  If given and not equal "." static files are not coppied,
as this indicates that they are not read from the the directory where
we'd copy them.  The default value is ".".

Merge pull request #1372 from haskell/dependabot/npm_and_yarn/haddock-api/resources/html/yargs-parser-5.0.1

Bump yargs-parser from 5.0.0 to 5.0.1 in /haddock-api/resources/html

Bumps [yargs-parser](https://github.com/yargs/yargs-parser) from 5.0.0 to 5.0.1.
- [Release notes](https://github.com/yargs/yargs-parser/releases)
- [Changelog](https://github.com/yargs/yargs-parser/blob/v5.0.1/CHANGELOG.md)
- [Commits](https://github.com/yargs/yargs-parser/compare/v5.0.0...v5.0.1

)

Signed-off-by: dependabot[bot] <support@github.com>

Bump y18n from 3.2.1 to 3.2.2 in /haddock-api/resources/html

Bumps [y18n](https://github.com/yargs/y18n) from 3.2.1 to 3.2.2.
- [Release notes](https://github.com/yargs/y18n/releases)
- [Changelog](https://github.com/yargs/y18n/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yargs/y18n/commits

)

Signed-off-by: dependabot[bot] <support@github.com>

Allow optparse-applicative 0.16 and tree-diff 0.2

Builds fine and all tests pass here.

Merge pull request #1361 from haskell/dependabot/npm_and_yarn/haddock-api/resources/html/elliptic-6.5.4

Bump elliptic from 6.5.3 to 6.5.4 in /haddock-api/resources/html

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.5.3 to 6.5.4.
- [Release notes](https://github.com/indutny/elliptic/releases)
- [Commits](https://github.com/indutny/elliptic/compare/v6.5.3...v6.5.4

)

Signed-off-by: dependabot[bot] <support@github.com>

Release 

Update Hackage index to 2021-03-02T19:46:27Z

Specify ghc-9.0.1 explicitly in cabal.project for CI

Select Cabal 3.4.0.0 instead of 3.4 in CI

Explicit import lists for Haddock.Interface and Haddock.Interface.Create

Clean-up of Interface and Interface.Create's imports part 2

Clean-up of Interface and Interface.Create's imports and pragmata

html-test: Always set language

from ghc-9.2 on, the “default” langauge of GHC is expected to change
more wildly. To prepare for that (and unblock
ghc!4853), this sets the
language for all the test files to `Haskell2010`. This should insolate
this test suite against changes to the default.

Change the CI badge to GH Actions

closes #1300

Fix 1261: replace dead links in docs

Make haddock more robust to changes to the `Language` data type

With the introduction of GHC2021, the `Languages` data type in GHC will
grow. In preparation of that (and to avoid changing haddock with each
new language), this change makes the code handle extensions to that data
type gracefully.

(cherry picked from commit c341dd7c)

Add -Wcompat-unqualified-imports flag

Clarify build instructions are for ghc-9.0 branch