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>

libc/include/sys/stat.h

@@ -0,0 +1,42 @@
+/*
+ * sys/stat.h — POSIX-style stat() / fstat() over ESTEX file metadata.
+ *
+ *   stat(path, &st)   queries via ESTEX F_FIRST ($19) using the exact
+ *                     name; gets size, attrib, and DOS-format date/time
+ *                     that we expand to a struct stat.
+ *   fstat(fd, &st)    queries an open handle: size via lseek(SEEK_END)
+ *                     trick + date/time via ESTEX GET_D_T ($17).
+ *
+ * Sprinter has no inodes / owners / groups, so st_ino / st_uid / st_gid
+ * are absent.  S_ISREG and S_ISDIR are the only meaningful mode tests.
+ */
+
+#ifndef SYS_STAT_H
+#define SYS_STAT_H
+
+#include <stdint.h>
+#include <time.h>      /* time_t */
+
+/* File mode bits — POSIX subset (octal as per convention). */
+#define S_IFMT     0170000      /* file-type mask */
+#define S_IFREG    0100000      /* regular file   */
+#define S_IFDIR    0040000      /* directory      */
+
+#define S_IRUSR    0000400      /* owner read     */
+#define S_IWUSR    0000200      /* owner write    */
+#define S_IXUSR    0000100      /* owner execute  */
+#define S_IRWXU    0000700
+
+#define S_ISREG(m)  (((m) & S_IFMT) == S_IFREG)
+#define S_ISDIR(m)  (((m) & S_IFMT) == S_IFDIR)
+
+struct stat {
+    uint16_t st_mode;       /* file type + perms */
+    uint32_t st_size;       /* size in bytes     */
+    time_t   st_mtime;      /* last-mod time (Unix epoch) */
+};
+
+int stat (const char *path, struct stat *buf);
+int fstat(int fd, struct stat *buf);
+
+#endif