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3.8 mb of sources duplicated from stage to stage and already superseded.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, 20 deletions

diff --git a/docs/history/13-gap-fixes/code/tests/gc.zc b/docs/history/13-gap-fixes/code/tests/gc.zc
deleted file mode 100644
index 41f14a0..0000000
--- a/docs/history/13-gap-fixes/code/tests/gc.zc
+++ /dev/null
@@ -1,20 +0,0 @@
-let keep;
-unchecked fn churn(n)
-{
-	let i = 0, p;
-	while (i < n) { p = new(10); p[0] = i; if (i % 100 == 0) keep = p; i++; }
-	return 0;
-}
-fn main()
-{
-	let base = live_objects(), f;
-	churn(1000);
-	putn(live_objects() - base); putc(' ');
-	f = gc();
-	putn(f >= 990); putc(' ');		// conservative: a stale word or two may keep one alive
-	putn(keep[0]); putc(' ');		// the one a global still points at survives
-	churn(200000);				// 3.2m words through a 393k word heap: needs the automatic collector
-	putn(gc_runs > 1); putc(' ');
-	putn(keep[0]); putc(10);
-	return 0;
-}