Split fields related functionality out of `Distribution.Parsec`
namespace which is not left only to handle "scalar" values.
This separation highlights that we use `parsec` for *structure* (think
JSON), and the *values* of the fields (think e.g. dates in JSON).

- New top-level `Distribution.Fields` and `Distribution.Parsec` modules
  should include most things most people would need.
- Also `Distribution.Pretty.Field` is moved to `Distribution.Fields.Pretty`,
  as now it has proper place.
- The commit is moving things around and fixing compilation errors.
- I fixed `cabal check` parse error printing as I was nearby.

Add hacked the --cwd argument parsing to
parser-tests and check-tests. It's a kludge
but it's good enough.

- Disable cabal-install's haddock on CI
- Temporarily disable cabal check (`-main-is` in tests)
- Remove this is not a lib note
- Tell to run git update-index --assume-unchanged

    ... when changing to -dev or -monolithic configuration.

    Run --no-assume-unchanged unconditionally, when
    changing to the production build.
- Improve auto-gen note in cabal-install.cabal
- Try to build haddock (with GHC-8.4.3 only)

Fixes #5086

The https://github.com/haskell/cabal/pull/5054 links to
https://github.com/commercialhaskell/stack/issues/3789 which says

- `Ensure you have OverloadedStrings and RebindableSyntax extensions
  enabled.`

So we warn only in that case. Only `OverloadeStrings` (or
`OverloadedLists`) or `RebindableSyntax` seems to be ok.

Also make `allBuildInfos` return all (not only buildable) build infos,
removing FIXME. `allBuildInfos` is used only in D.PD.Check.

Solves #5087
Related to #5003

Note: `buildable: ` field has `All` semantics. `scope: ` has
`AnyPrivate` semantics. Both might be surprising, but are "logical".

https://hackage.haskell.org/package/Cabal-2.0.1.1/docs/src/Distribution.PackageDescription.Parse.html#line-248

Distribution.SDPX.LicenseId and Distribution.SDPX.LicenceExceptionId are
generated.

This is poor man doctest.

Prerequisites:
- `doctest` executable is in `$PATH`, compiled with GHC used to
  new-build the Cabal
- `.ghc.environment` file is generated

As GHC picks up dependencies from `.ghc.environment` file, a simple
`doctest MODULES` works.

As you see, I had a bug in doctests. For now, I don't add this to CI,
as it's enough to run doctests occasionally (there are only 4 examples
atm).

At the moment we have very lax "name" lexer, which is essentially
*everything else* than otherwise specified characters: parens, space,
symbols (but not hyphen -)

This removes `TokNum` and `SecArgNum`, both are merged into `TokSym` and
`SecArgSym` respectively.

- Manually generate Lexer.hs
- Temporarily disable parser-hackage-tests on appveyor (needs
  01-index.tar)
- Add root Makefile to handle commmon dev tasks (genering Lexer.hs)

At the top level we now have cabal/ and cabal-install/

The chapter on installing packages still needs to be rewritten
to describe the cabal tool, rather than runhaskell Setup.hs

Means we only need to have the version in one place now. Yay.

Useless docbook tools.

The 1.8.x branch remains at 1.8.0.1

A few changes since version 1.8.0 that was released with ghc-6.12rc1

Add an explicit intermediate ProgramInvocation data type.

Apparently xsltproc does not validate against the dtd.
This should stop errors creaping back in.

As it says in http://docbook.sourceforge.net/release/xsl/current/README:

  - Use the base canonical URI in combination with one of the
    pathnames below. For example, for "chunked" HTML, output:

    http://docbook.sourceforge.net/release/xsl/current/html/chunk.xsl

This is to work around the file permissions problems with the
standard System.Directory.copyFile function. When installing
files we do not want to copy permissions or attributes from the
source files. On unix we want to use specific permissions and
on windows we want to inherit default permissions. On unix:
copyOrdinaryFile   sets the permissions to -rw-r--r--
copyExecutableFile sets the permissions to -rwxr-xr-x

Building the haddock docs requires building first. Arguably this is
a Cabal bug. It should probably generate the "autogen" files for
haddock and not just for build.

It did not actually contain any release notes and just
duplicated information in the README which was confusing.

To make easier to track recent Cabal / cabal-install changes