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>

docs/reference/SPRINT2K/SPRN2K11.TXT

@@ -0,0 +1,32 @@
+*** Area: ZX.SPECTRUM                             Date: 31 Mar 01  5:15:30
+*** From: Ivan Mak (2:5030/529.24)
+*** To  : Nikolay G.Arhipoff
+*** Subj: Ž ‘¯p¨­â¥p¥.
+
+
+        �ਢ¥âáâ¢ãî ‚ á, Nikolay!
+
+  <Friday March 30 2001> <13:03> Nikolay G.Arhipoff wr®te to Ivan Mak:
+
+ NA> H¥ ⮫쪮... �à¨ç¨­ ­¥áª®«ìª® - ­ ¯à á 䨭 ­á ¬¨, ¯à¨§ë¢ ¢  à¬¨î,
+ NA> ¬ «® á®äâ . ‘ ¬ ï £« ¢­ ï - à §£à®¬­ ï áâ âìï ¢ ª ª®¬-â® ¦ãà­ «¥, çâ®
+ NA> íâ®â ª®¬¯ ¯«®å® áâëªã¥âáï á ¯¥à¨ä¥à¨¥© ¨ ¢á¥ ¯à¨å®¤¨âáï ¯®¤¡¨à âì ¤«ï
+ NA> ª®­ªà¥â­®© ¬®¤¥«¨ ª®¬¯  ª ª-â® ¬ëè , ª« ¢ª  ¨ â.¤.
+
+‚®â íâ  áâ âìï ®â 祫®¢¥ª , ª®â®pë© ¡ë« 㢮«¥­ ¨§ �¥â¥pá  ¨ p¥è¨« ­ á®«¨âì.
+‚ ­¥© ®âªp®¢¥­­®¥ _¢p ­ì¥_, ¨ ®¡ í⮬ ï 㦥 ¯¨á «. —¥«®¢¥ª â®â ª ‘¯p¨­â¥pã
+¨¬¥« ­¥ ¡®«ìè¥ ®â­®è¥­¨ï 祬 ᢨ­ìï ª  ¯¥«ìᨭ ¬... Ž­ ¢®®¡é¥ _ ¬¨¦­¨ª_!
+
+�®¤¡¨p âì ¯p¨å®¤¨«®áì ⮫쪮 ¤¨ª®-áâ pë¥ ¢¨­âë, ª®â®pë¥ ¨ ­  �– ¯®«®¢¨­  ­¥
+§ ¢®¤¨«¨áì. ‘ ª« ¢¨ âãp®© ¨ ¬ëè ¬¨ á¥p쥧­ëå ¯p®¡«¥¬ ¢®¢á¥ ­¥ ¡ë«®,   ¨§
+­¥á¥p쥧­ëå ⮫쪮 ⥠¯«®å® p ¡®â «¨, çâ® á ¬¨ ¯® ᥡ¥ ¯®«ã¤®å«ë¥ ¡ë«¨...
+
+Ž ⮬, çâ® ¦ãp­ « SE ¢ë¯ã᪠«áï ª®­ªãp¥­â ¬¨, ¨ £®¢®p¨âì ­¥ç¥£®...
+
+        �à®â®áë á¡¥¦ «¨. ‡¥à£¨ § ª®¯ «¨áì. �®à  ¨ ¬­¥ § ªà㣫ïâìáï. Ivan.
+
+  - � §¢®¤¨áì á奬ª , ¡®«ìè  ¨ ¬ «¥­ìª ... [ Sprinter-II ] [Forth-CPU] [ZX]
+
+... ivan_mak@mail.ru * http://st-rektal.chat.ru * http://www.atlant.ru/peters
+--- GoldED+/386 1.0.0
+ * Origin: The Sprinter has You! (2:5030/529.24)