v4.0.0

• Make sure the psqueues Haskell package gets the fingertree-psqueue dep
  depending on what version of psqueues you're compiling.

  Added in #39.

• Change stacklock2nix's handling of Stack's git dependencies.

  A git dependency looks like the following in stack.yaml:

  extra-deps:
    - git: "https://github.com/haskell-servant/servant-cassava"
      commit: "f76308b42b9f93a6641c70847cec8ecafbad3abc"

  Up until now, stacklock2nix would download Stack's git dependencies using
  Nix's builtins.fetchGit function.

  By default, this function doesn't clone the full repository, but only the
  history of the default branch. This is a problem if you try to specify a
  commit that is not a parent of the default branch. This may happen if
  you're developing new functionality in a feature branch that hasn't yet
  been merged into master.

  stacklock2nix has been changed to additionally specify the allRefs = true
  argument to builtins.fetchGit. This causes the full Git repository to be
  downloaded, even commits that aren't ancestors of the default branch.

  Added in #39.
  Thanks to @isomorpheme for reporting this
  and coming up with the fix.

  It is possible this causes increased download times, especially for repos
  that are very big.

  You may be able to work around this by using Stack's functionality for
  downloading given URLs, in order to download a tarball of a repository
  (without any of the Git history).:

  extra-deps:
    - url: "https://github.com/haskell-servant/servant-cassava/archive/f76308b42b9f93a6641c70847cec8ecafbad3abc.tar.gz"