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3.8 mb of sources duplicated from stage to stage and already superseded.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, 35 deletions

diff --git a/docs/history/13-gap-fixes/code/examples/lists.zc b/docs/history/13-gap-fixes/code/examples/lists.zc
deleted file mode 100644
index 6ac276e..0000000
--- a/docs/history/13-gap-fixes/code/examples/lists.zc
+++ /dev/null
@@ -1,35 +0,0 @@
-// ownership in practice: a list owns its boxes. nothing here calls free;
-// everything is released at the end of the block that owns it.
-fn box(v) -> .u { let b = new(1); b[0] = v; return u*b; }
-fn mklist(cap) -> .u { let l = new(cap + 1); l[0] = 0; return u*l; }
-// item m*arrives (it was given down), and goes d*on into the borrowed list
-fn push(.m l, .d item) { l[l[0] + 1] = d*item; l[0] = l[0] + 1; return 0; }
-fn show(.m l)
-{
-	let i = 1;
-	putc('[');
-	while (i <= l[0]) { if (i > 1) putc(' '); putn(l[i][0]); i++; }
-	putc(']');
-	return 0;
-}
-fn squares(n) -> .u
-{
-	let l = mklist(n), i = 0;
-	while (i < n) {
-		let b = box(i * i);
-		push(l, d*b);
-		i++;
-	}
-	return u*l;
-}
-fn main()
-{
-	let before = live_objects();
-	{
-		let l = squares(6);
-		show(l); putc(10);
-		puts("live: "); putn(live_objects() - before); putc(10);
-	}
-	puts("after the block: "); putn(live_objects() - before); putc(10);
-	return 0;
-}