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>

examples/stest2/stest2.c

@@ -0,0 +1,43 @@
+/*
+ * stattest — exercise POSIX stat() and fstat() over ESTEX file metadata.
+ *
+ * Calls:
+ *   stat() on a file by path
+ *   stat() on a directory (current dir)
+ *   stat() on a non-existent file (expects errno=ENOENT)
+ *   fstat() on a freshly opened file
+ */
+
+#include <stdio.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <time.h>
+#include <dir.h>
+
+
+int main(int argc, char **argv)
+{
+    struct stat st;
+
+    puts("stattest: stat() / fstat() smoke test");
+
+    ffblk_t ffb;
+
+    if (ffirst(argv[0], &ffb, FA_DIREC) == 0) {
+        printf("File %s, size = %d\n", argv[0], ffb.size);
+    } else {
+        printf("File %s, error\n", argv[0]);
+    }
+
+    if (argc > 1) {
+        if (ffirst(argv[1], &ffb, FA_DIREC) == 0) {
+            printf("File %s, size = %d\n", argv[1], ffb.size);
+        } else {
+            printf("File %s, error\n", argv[1]);
+        }
+    }
+    return 0;
+}