build: use small patch files by default; add --seed option

`egads build` makes a small patch file against a known git tag.

Added an `egads build --seed` option to build a complete tarball and
tag to make patches against.
extract: support patches and seed builds
build: fix egads-seed file contents in patches
extract: don't mark seeds as extracted
extract: fix seed extraction
Atomically symlink directories (e.g., during release)
extract: do it right?
build: tweaks
build: record parent SHA of seed tag in patches
extract: fix tests
extract: fix say => say_status
extract: fix patch level
extract: add -f alias
stage: fix symlinks
release: move atomic_symlink method to release
extract: use `git apply` instead of `patch`

For binary file support
trim: delete old seeds
capistrano: build locally instead of waiting
fix docs
Merge pull request #1 from kickstarter/patches

Support smaller builds with patches and seeds