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/STRING.H

@@ -0,0 +1,33 @@
+/*
+ *	STRING.H
+ *
+ *	String manipulation functions.
+ *	(c) 2004, SOLID C  Sprinter-2000
+ */
+
+
+#ifndef	_C_TYPES_
+#include <types.h>
+#endif
+
+
+void *memchr();			/* search for a character in memory block */
+char *strcat();
+char *strncat();
+char *strchr();
+int  strcmp();
+int  strncmp();
+char *strcpy();
+char *strncpy();
+size_t strcspn();
+size_t strlen();
+char *strlwr();
+char *strpbrk();
+char *strrchr();
+size_t strspn();
+char *strstr();
+char *strtok();
+char *strupr();
+char *strerr();
+
+#define strerror   strerr;