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/solid-c/INCLUDE/IO.H

@@ -0,0 +1,51 @@
+/*
+ *	IO.H
+ *
+ *	Low-level nonbuffered file I/O.
+ *	(c) 2004, SOLID	C  Sprinter-2000
+ */
+
+
+#ifndef	_C_TYPES_
+#include <types.h>
+#endif
+
+#ifndef	_STD_LIB_
+#include <stdlib.h>
+#endif
+
+
+#ifndef	_STD_SEEK_
+#define	_STD_SEEK_
+/* constants to be used as 3rd argument for "fseek" function */
+#define	SEEK_SET	0
+#define	SEEK_CUR	1
+#define	SEEK_END	2
+#endif
+
+
+/* Definition "open flags" */
+#define	O_WRONLY	0x01		/* 0  file write only */
+#define	O_RDONLY	0x02		/* 1  file read only */
+#define	O_RDWR		0x03		/* 1,0 file read/write */
+#define	O_TRUNC		0x04		/* 2  open with truncation */
+#define	O_CREAT		0x08		/* 3  create and open file */
+#define	O_EXCL		0x10		/* 4  exclusive open */
+#define	O_APPEND	0x20		/* 5  to end of file */
+
+
+
+uint open();			/* opens/creates a file */
+uint creat();			/* creates file */
+size_t read();			/* read file */
+size_t write();			/* write file */
+uint close();			/* close file */
+uint seek();			/* sets file pointer (range 0..65534) */
+uint tell();			/* returns current position (range 0..65534) */
+struct fpoint *lseek();		/* sets file pointer */
+struct fpoint *ltell();		/* returns current position */
+char unlink();			/* delete file */
+char remove();			/* delete file */
+char rename();			/* rename file */
+BOOL isatty();			/* return "true" if FD is console I/O */
+int ioctl();			/* control i/o for devices or files */