docs: archive the frozen stage code as one compressed tarball

docs/history kept six stages with a full copy of the project under code/,
3.8 mb of sources duplicated from stage to stage and already superseded. store
them as docs/history/code-snapshots.tar.gz, 0.66 mb, and extract one in place
to read it. every stage's notes.md stays browsable, and the index says where the
code went and how to get it back.

the top-level README points at the archive too. its other two links into
docs/history, 21-micro and 35-bench, were notes that were never kept and do not
resolve; the index now records that.

1 files changed, 0 insertions, 4 deletions

diff --git a/docs/history/13-gap-fixes/code/examples/fact.zc b/docs/history/13-gap-fixes/code/examples/fact.zc
deleted file mode 100644
index 2a218b2..0000000
--- a/docs/history/13-gap-fixes/code/examples/fact.zc
+++ /dev/null
@@ -1,4 +0,0 @@
-fn fact(n) { if (n < 2) return 1; return n * fact(n - 1); }
-// prints in binary, like the old asm example
-fn bin(n) { if (n > 1) bin(n >> 1); putc('0' + (n & 1)); return 0; }
-fn main() { bin(fact(10)); putc(10); putn(fact(10)); putc(10); return 0; }