This directory contains software that is used in bayeslite but written
and maintained externally by someone else.  We will use the following
organization in order to:

- Use external software that is not in Ubuntu and does not use Git.
- Keep history of our updates to external software.
- Make local changes as we need and send patches upstream.
- Merge our local changes into external updates.
- Avoid imposing the mess of submodules on users.

* Directory layout:

Each subdirectory corresponds to one external package and has the
following contents:

COPYING         summary of copying terms
dist/           subdirectory containing the external distribution
prepare.sh      script to prepare a distribution for import
...             other supporting files

prepare.sh should run in the top-level directory of the external
distribution, which will then be imported under dist/.  It should only
do clean-ups necessary to make the distribution fit for inclusion in
our tree, such as deleting binary files.  Local changes, such as bug
fixes, should be made in separate commits.

* To import a new external package:

1. Write the COPYING file and prepare.sh script and commit them.

2. Create a temporary Git repository for the package:

      % cd /tmp
      % mkdir repo
      % cd repo
      % git init

3. Extract proj-1.2 in external/proj/dist in the temporary repository:

      % mkdir -p external/proj
      % cd external/proj
      % gunzip -c < /tmp/proj-1.2.tar.gz | tar xf -
      % mv proj-1.2 dist

4. Run the prepare.sh script:

      % (cd dist && sh /path/to/bayeslite/external/proj/prepare.sh)

5. Commit the result in the temporary repository:

      % git add dist
      % git commit

   The commit message should summarize what proj is, specify where
   proj-1.2.tar.gz came from, and give its SHA-256 hash.

6. In the main repository, create a vendor branch and release tag:

      % cd /path/to/bayeslite
      % git fetch /tmp/repo master:vendor/proj
      % git tag vendor/proj-1.2 vendor/proj

7. Merge proj-1.2 into the branch you're working on:

      % git merge vendor/proj-1.2

8. Push the vendor branch upstream so others can use it:

      % git push origin vendor/proj

* To see what version we have most recently merged:

% git log --merges external/proj

Note: This requires that every `git merge' involved use the release
tag (vendor/proj-1.2), not the vendor branch (vendor/proj).
Everything else will work if you use the vendor branch, so be careful.

Note: You can't use `git log --merges external/proj/dist', apparently:
it skips the very first merge.  Go figure.

* To see what local changes there are in a external package:

% git diff vendor/proj-1.2 HEAD -- ./external/proj
% git show vendor/proj-1.2..HEAD -- ./external/proj/dist

* To update an existing external package:

1. Update prepare.sh and check for changes to copying terms.

2. Check out the vendor branch in an empty clone of the repository:

      % git clone --no-checkout -b vendor/proj /path/to/bayeslite /tmp/repo

3. Extract proj-1.3 in external/proj/dist in the clone:

      % cd /tmp/repo
      % mkdir -p external/proj
      % cd external/proj
      % gunzip -c < /tmp/proj-1.3.tar.gz | tar xf -
      % mv proj-1.3 dist

4. Run the prepare script:

      % (cd dist && /path/to/bayeslite/external/proj/prepare.sh)

4. Commit and tag the update:

      % git add --all dist
      % git commit
      % git tag vendor/proj-1.3

5. In the main repository, update the vendor branch and tag it:

      % cd /path/to/bayeslite
      % git fetch /tmp/repo vendor/proj
      % git tag vendor/proj-1.3 vendor/proj

6. Finally, merge the new release tag:

      % git merge vendor/proj-1.3
