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/stdio.h

@@ -0,0 +1,102 @@
+/*
+ * stdio.h — extends SDCC's z80 stdio with a minimal FILE * stream API.
+ *
+ * The bottom of the stack is the existing POSIX-style fd I/O (open/
+ * read/write/close/lseek).  FILE * is a thin struct wrapping a fd plus
+ * a few flag bits.  No buffering — every fread/fwrite/fputc maps 1:1
+ * to a syscall.  Sprinter's I/O is already char-oriented at the ESTEX
+ * level, so this stays minimal.
+ *
+ * stdin / stdout / stderr are predefined "virtual" FILE * pointers
+ * that talk to the console via putchar()/getchar() (NOT through a fd).
+ * That keeps printf-routed output going through our CR/LF mapping.
+ */
+
+#ifndef STDIO_H
+#define STDIO_H
+
+#include <stdarg.h>
+#include <stddef.h>      /* size_t */
+#include <stdint.h>
+
+#ifndef EOF
+#define EOF (-1)
+#endif
+
+/* ---- printf family (linked from SDCC's z80.lib) -------------------- */
+int  printf (const char *, ...);
+int  sprintf(char *, const char *, ...);
+int  vprintf(const char *, va_list);
+int  vsprintf(char *, const char *, va_list);
+
+/* puts / putchar / getchar — overridden by our libc to use ESTEX. */
+int  puts   (const char *);
+int  putchar(int);
+int  getchar(void);
+
+/* ---- FILE * (minimal, unbuffered) ---------------------------------- */
+
+/* Internal layout — opaque to user.  fd == -1 marks the console
+ * pseudo-streams (stdin/stdout/stderr). */
+typedef struct __FILE {
+    int     fd;          /* underlying POSIX fd, or -1 for console */
+    uint8_t flags;       /* see _F_* below */
+} FILE;
+
+#define _F_READ    0x01
+#define _F_WRITE   0x02
+#define _F_APPEND  0x04
+#define _F_EOF     0x10
+#define _F_ERROR   0x20
+#define _F_CONIN   0x40  /* console pseudo-stream — uses getchar() */
+#define _F_CONOUT  0x80  /* console pseudo-stream — uses putchar() */
+
+extern FILE *const stdin;
+extern FILE *const stdout;
+extern FILE *const stderr;
+
+/* fseek whence — same numeric values as SEEK_SET/CUR/END in unistd.h. */
+#ifndef SEEK_SET
+#define SEEK_SET 0
+#define SEEK_CUR 1
+#define SEEK_END 2
+#endif
+
+FILE  *fopen (const char *path, const char *mode);
+int    fclose(FILE *fp);
+int    fflush(FILE *fp);
+
+int    fputc (int c, FILE *fp);
+int    fgetc (FILE *fp);
+int    fputs (const char *s, FILE *fp);
+char  *fgets (char *buf, int n, FILE *fp);
+
+size_t fread (void *ptr, size_t size, size_t nmemb, FILE *fp);
+size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *fp);
+
+int    fseek (FILE *fp, long off, int whence);
+long   ftell (FILE *fp);
+void   rewind(FILE *fp);
+
+int    feof  (FILE *fp);
+int    ferror(FILE *fp);
+void   clearerr(FILE *fp);
+
+/* Aliases to fputc/fgetc — POSIX says they may be macros. */
+#define putc(c, fp)   fputc(c, fp)
+#define getc(fp)      fgetc(fp)
+
+/* Read line from stdin into buf until '\n' or EOF; '\n' is not stored.
+ * Returns buf, or NULL on EOF with empty input.  Solid-C/POSIX semantic.
+ * Note: dangerous, no length check — caller must size buf appropriately. */
+char *gets(char *buf);
+
+/* Solid-C decimal/hex helpers — print uint as decimal/hex without args. */
+void hex8 (uint8_t  v);   /* prints two hex digits */
+void hex16(uint16_t v);   /* prints four hex digits */
+void hex32(uint32_t v);   /* prints eight hex digits */
+void dec8 (uint8_t  v);   /* prints up to 3 decimal digits, no padding */
+void dec16(uint16_t v);   /* prints up to 5 decimal digits */
+void dec32(uint32_t v);   /* prints up to 10 decimal digits */
+
+#endif