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3.8 mb of sources duplicated from stage to stage and already superseded.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, 28 deletions

diff --git a/docs/history/15-o3/code/examples/tree.zc b/docs/history/15-o3/code/examples/tree.zc
deleted file mode 100644
index 90a01d4..0000000
--- a/docs/history/15-o3/code/examples/tree.zc
+++ /dev/null
@@ -1,28 +0,0 @@
-// a binary search tree where every node owns its children. there's no free
-// anywhere: when the root's block ends, the whole tree goes with it.
-struct node { int v; *node left, right; };
-
-*node.u leaf(int v) { *node n = new(node); n.v = v; return u*n; }
-// n is borrowed; storing a new leaf into it makes n the leaf's owner
-fn insert(*node.m n, int v)
-{
-	if (v < n.v) { if (n.left) insert(n.left, v); else n.left = leaf(v); }
-	else { if (n.right) insert(n.right, v); else n.right = leaf(v); }
-	return 0;
-}
-fn walk(*node n) { if (!n) return 0; walk(n.left); putn(n.v); putc(' '); walk(n.right); return 0; }
-int height(*node n) { if (!n) return 0; int l = height(n.left), r = height(n.right); return 1 + (l > r ? l : r); }
-
-fn main()
-{
-	let before = live_objects();
-	{
-		*node root = leaf(50);
-		int x = 7;
-		for (int i = 0; i < 30; i++) { x = (x * 37 + 11) % 100; insert(root, x); }
-		walk(root); putc(10);
-		puts("height "); putn(height(root)); puts(", live objects "); putn(live_objects() - before); putc(10);
-	}
-	puts("after the block: "); putn(live_objects() - before); putc(10);
-	return 0;
-}