Barn 0.1.0

Added

• barn hatch, install, add, remove, upgrade, verify, lay and inspect, whose
  --flat lists the eggs a project uses.
• barn.json, strict JSON, with dependencies and overrides, which add, remove and
  upgrade rewrite. There is no lock file: the versions follow from barn.json, and the
  SHA-256 sums of each egg live in ~/.barn/eggs.
• Minimal version selection: each egg gets the newest version asked for, and incompatible
  versions are an error.
• A local eggs folder with immutable releases and snapshots: ~/.barn/eggs, or eggs/
  under BARN_HOME. The commands that install or lay eggs create it when it is missing.
  Snapshots sit beside their release as 0.1.0_snapshot_<stamp>_<hash>, named by the time
  they were laid and their content.
• 0.1.0 asks for that release only, never a snapshot of it; 0.1.0_snapshot asks for the
  newest snapshot.
• Prebuilt executables for Linux, macOS and Windows on each GitHub release.
• barn build and barn run, which stop when a copy in .barn/ is not the version
  barn.json asks for or differs from its sums in ~/.barn/eggs, and otherwise hand the project to goose build or
  goose run.
• barn test, which does the same checks and then runs test/main_test.goose, or the file
  test names in barn.json. barn hatch writes the test file, and barn install updates
  its imports as it does those of main.goose.
• Eggs laid from the project folder, or from the folder source names: <name>.goose at
  its top, the other files under it, and LICENSE and README. Tests, examples, benches,
  docs, dot-files, the main and test files and whatever exclude lists stay out, and in a
  git repository so do the files git ignores.
• barn hatch makes an egg with <name>.goose at the top; barn hatch --app adds
  main.goose.
• barn lay --release tags the commit v<version> in a git repository with nothing left to
  commit, stores the release with a barn.origin file and asks before pushing the tag to
  origin. Without origin, or when the answer is no, the release stays on this machine.
• install, add, remove and upgrade fetch missing releases from their git repository,
  and ~/.barn/config.json can point a host at a mirror.
• add and upgrade find releases on the repository too, and refuse a tag that has moved
  since it was fetched.
• "local_priority": false, --set local_priority=... for one command, and --offline.
• barn install --force fetches a release that was changed in the eggs folder again from
  its repository, after checking that its tag has not moved; a changed snapshot asks to be
  deleted and laid again.
• Snapshots fetched from their repository's commits: 0.1.0_snapshot takes the newest
  commit on the default branch whose barn.json says 0.1.0, and an exact
  0.1.0_snapshot_<stamp>_<hash> the commit it names. Snapshots laid on this machine come
  first unless local priority is off, and an unreachable repository falls back to the
  snapshots already here with a warning.
• A token for each host in ~/.barn/config.json, with an optional user, sent to that
  host only as HTTP basic authentication. Barn passes it to git in the environment rather
  than on the command line.
• Plain Goose libraries without barn.json install as eggs with no dependencies, named
  after the one <name>.goose at their top that declares namespace <name>;.
• Eggs named by their repository, acme/numbers or gitlab.com/acme/tools, and imported
  under the name in their barn.json; "repo" says where a project lives when that
  differs from <owner>/<name>. The eggs folder keeps them under their host.
• barn lay --check, which checks the egg and lists its files without laying it, and a
  warning when a file in the egg names where a dependency comes from.
• Owners with uppercase letters, from --owner, BARN_OWNER, barn.json or add, remove
  and upgrade, are lowercased with a warning. Egg names stay lowercase only, since they are
  folder and import names; an uppercase one is an error that suggests the lowercase spelling.
• A failed fetch says why, with the reason git gave. Fetching works with a deep BARN_HOME
  on Windows: the temporary folders have short names, and git runs with core.longpaths on.