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3.8 mb of sources duplicated from stage to stage and already superseded.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, 13 deletions

diff --git a/docs/history/15-o3/code/tools/build.zc b/docs/history/15-o3/code/tools/build.zc
deleted file mode 100644
index a38e97f..0000000
--- a/docs/history/15-o3/code/tools/build.zc
+++ /dev/null
@@ -1,13 +0,0 @@
-// compiles the rest of stdin (after the backtick) as a genome image at GORG
-// and writes it to stdout as little-endian 32-bit words.
-const OUT = 0x10000;
-fn main()
-{
-	let n = build_image(GORG, OUT), i = 0, w;
-	while (i < n) {
-		w = OUT[i];
-		putc(w); putc(w >> 8); putc(w >> 16); putc(w >> 24);
-		i++;
-	}
-	return 0;
-}