Add full compiler toolchain, libc, examples and reference docs

First substantive commit: the entire Sprinter C compiler tree on top of
the bare README+gitignore initial commit.

What's in here:
  bin/sprinter-cc        — driver script invoking SDCC + linker + mkexe
  libc/                  — Sprinter-specific libc layer over ESTEX/BIOS
                           (conio, gfx, io, mem, stdio + headers)
  runtime/               — crt0 variants (default/small/banked/minimal)
                           + heap + bank trampolines
  toolchain/             — mkexe (SprintEXE packer, C + tests)
  examples/              — 30 demo programs (gfx, file I/O, env, time, …)
  lib/Makefile           — builds the libc archive (sprinter.lib)
  docs/                  — converted Sprinter manuals + asm reference samples
  third_party/           — solid-c reference compiler dump + sdcc setup script
  release_docs/          — packaging / release notes

gitignore overhaul:
  • Drop dangerous blanket patterns: *.asm (would hide docs/samples/*.asm)
    and *.exe (case-insensitive match was hiding third_party/solid-c/*.EXE
    on macOS APFS).  Replaced with examples/*/*.{asm,exe,…} and lib/*.lib.
  • Restore tracking of toolchain/mkexe/tests/{one,big}.bin — those are
    INPUT fixtures, not build outputs.
  • Collapse the duplicated SDCC/C/Sdcc sections into one section per
    concern (build outputs / vendored / OS-junk).
  • Add .sprinter-cc-*/, build/ (catches lib/build/ too), .claude/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

third_party/setup-sdcc.sh

@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+# Download and extract a vendored SDCC into third_party/sdcc-<VERSION>/.
+# Idempotent: re-running with the same version is a no-op.
+
+set -euo pipefail
+
+VERSION="${1:-4.5.0}"
+
+here="$(cd "$(dirname "$0")" && pwd)"
+cd "$here"
+
+uname_s=$(uname -s)
+uname_m=$(uname -m)
+
+case "$uname_s" in
+    Darwin)
+        archive="sdcc-${VERSION}-x86_64-apple-macosx.tar.bz2"
+        sf_dir="sdcc-macos-amd64"
+        if [ "$uname_m" = "arm64" ]; then
+            echo "Note: macOS binary is x86_64; on Apple Silicon it runs via Rosetta 2."
+            if ! /usr/bin/arch -x86_64 /usr/bin/true 2>/dev/null; then
+                echo
+                echo "Rosetta 2 is not installed. Install it with:"
+                echo "    softwareupdate --install-rosetta --agree-to-license"
+                echo
+                echo "Then re-run this script."
+                exit 4
+            fi
+        fi
+        ;;
+    Linux)
+        archive="sdcc-${VERSION}-amd64-unknown-linux2.5.tar.bz2"
+        sf_dir="sdcc-linux-amd64"
+        ;;
+    *)
+        echo "Unsupported host OS: $uname_s" >&2
+        exit 2
+        ;;
+esac
+
+dest="sdcc-${VERSION}"
+if [ -d "$dest" ] && [ -x "$dest/bin/sdcc" ]; then
+    echo "SDCC ${VERSION} already vendored at third_party/${dest}"
+else
+    url="https://sourceforge.net/projects/sdcc/files/${sf_dir}/${VERSION}/${archive}/download"
+    if [ ! -f "$archive" ]; then
+        echo "Downloading $archive..."
+        curl -fL -o "$archive.tmp" "$url"
+        mv "$archive.tmp" "$archive"
+    else
+        echo "Using cached $archive"
+    fi
+    echo "Extracting..."
+    rm -rf "$dest"
+    mkdir -p "$dest"
+    tar -xjf "$archive" --strip-components 1 -C "$dest"
+fi
+
+ln -sfn "$dest" sdcc
+
+echo
+echo "Verifying installed toolchain:"
+"$here/sdcc/bin/sdcc" --version 2>&1 | head -3 || {
+    echo
+    echo "Failed to run sdcc; if you saw 'Bad CPU type' run:"
+    echo "    softwareupdate --install-rosetta --agree-to-license"
+    exit 3
+}
+
+for tool in sdcc sdasz80 sdldz80 sdar sdobjcopy; do
+    if [ -x "$here/sdcc/bin/$tool" ]; then
+        echo "  found: bin/$tool"
+    else
+        echo "  MISSING: bin/$tool" >&2
+    fi
+done
+
+echo
+echo "Done. Toolchain at: third_party/sdcc -> $dest"