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/SPRN2K54.TXT

@@ -0,0 +1,63 @@
+*** Area: ZX.SPECTRUM                             Date: 26 Jun 137 11:45:13
+*** From: Denis Parinov (2:5030/529.48)
+*** To  : Andy Harchenko
+*** Subj: ...
+
+        � ¤ ¯à¨¢¥âá⢮¢ âì ⥡ï, Andy!
+
+   Monday May 21 2001 Andy Harchenko -> Denis Parinov.
+
+ AH> Don't cry, Denis!
+
+I won't cry!
+
+ DP>> áâ ­¥â ­¨ªâ®, â ª ¡¥á¯®ª®¨âìáï ¨§-§ 
+ DP>> ­¨ç¥£®¨§á¥¡ï­¥¯p¥¤áâ ¢«ïî饣® ª®¬¯ìîâ¥p .
+ DP>> P.S. H¨ç¥£® «¨ç­®£®, ¯p®áâ® ­¥å®ç¥âìáï ®â¢¥ç âì ­  ª ¦¤ë©
+ DP>> ¯®¤®¡­ë© ¢ë¯ ¤. “ ­ á ¬ áá  p ¡®âë, íâ® ¢ ¬ ­¥ PC, £¤¥ ¢á¥ ¥áâì ¨
+ DP>> "­  å «ï¢ã".
+ AH> ¢á¥£® âਠ¯ã­ªâ :
+ AH> 1) â¥å­¨ç¥áª ï ¯®¤¤¥à¦ª  ¯à¨ ¬¨­¨¬ «ì­ëå ãᨫ¨ïå á® áâ®à®­ë
+ AH> ¯®«ì§®¢ â¥«ï
+
+€«â¥p . ‚ᥠ¨§¬¥­¥­¨ï, bug-fix'¨, ­®¢ë¥ ¢®§¬®¦­®áâ¨, ¬®¦­® ¯®«ãç¨âì ¯®
+¨­â¥p­¥â.
+
+ AH>  2) ¬ áá  ¤¥è¥¢®£® ¯¨à â᪮£® á®äâ  ¨ «¨â¥à âãàë
+
+™ á, ¡ã¤ãâ ª¨¤ âì âãå«ë¬¨ ¯®¬¨¤®p ¬¨ :)
+­® ­¥ª®â®pë¥ ¯p¨§­ î, çâ® ‘¯¥ªâp㬮¢áª¨¥ ¨£pë ¨­®£¤  «ãçè¥.
+€ «¨â¥p âãpã ­ ¤® ç¨â âì ª ª ï áç¨â î ¯« âä®p¬®­¥§ ¢¨¬ãî. ’®«ªã ¡®«ìè¥ ¡ã¤¥â.
+•®âï ï ᮣ« á¥­ ᯥæ¨ä¨ç¥áª ï «¨â¥p âãp  ­ã¦­ .
+
+ AH>  3) ¢á¥¬¨à­®¯à¨§­ ­­ë© áâ ­¤ àâ
+
+¡ ­ «ì­® ZX Spectrum.
+
+ AH> 祬 ¬®¦¥â ®â¢¥â¨âì ‘¯à¨­â¥à ­  í⨠âਠ¯ã­ªâ ?
+
+  ¤®«¦¥­?
+
+ AH> §ë ¯à®è«¨ ⥠¢à¥¬¥­ , ª®£¤  ¬®¦£® ¡ë«® ᮡà âì ª®¬¯ ¢ £ à ¦¥, ¢ ¨â®£¥
+ AH> ᮧ¤ âì á¢®î ¯« âä®à¬ã ¨ ᪮«®â¨âì ­  ­¥© ®¤­ã ¨§ á ¬ëå ªà㯭ëå ä¨à¬ ¢
+ AH> ¬¨à¥.
+
+„ , ­¨ªâ® ¨ ­¥ £®¢®p¨â, ¯p® â®, çâ® ¬ë ᮡ¨p ¥¬áï ª®«®­¨§¨p®¢ âì £ « ªâ¨ªã.
+Œë §¤¥« «¨ ª®¬¯ìîâ¥p, ᮢ¬¥áâ¨¬ë© á® ‘¯¥ªâp㬮¬ ª ª®â®p®¬ã ¯®¤«îç îâìáï
+áâ ­¤ pâ­ë¥ ¢¨­ç¥áâ¥pë, ᨤ¨p®¬ë, ¬®¤¥¬ë, ¤¨áª®¢®¤ë, ª« ¢¨ âãpë, ¬ëè¨.
+ˆ ᮡ¨p ¥âìáï ¡¥§ ¯ ï«ì­¨ª . „  ®­ ¨¬¥¥â ­¥ª®â®pë¥ ã­¨ª «ì­ë¥ ¢®§¬®¦­®á⨠­¥
+¯p¥¤áâ ¢«¥­­ë¥ ­  ¤pã£¨å ¯« âä®p¬ å.
+
+ AH> Sprinter vs PC or Sprinter vs Mac íâ® ¢®§¬®¦­® ⮫쪮 ¥á«¨ ã ¢ á
+
+  íâ® ªáâ â¨ ª ª p § ­ ®¡®p®â, ­ ¬ ¯ëâ îâáï ­ ¢ï§ âì áp ¢­¥­¨¥.
+Ÿ ¢á¥£¤  ¯¨á «, çâ® ¥á«¨ 祫®¢¥ªã H“†…H PC, â® ï ­¥ áâ ­ã ¥¬ã ¯p¥¤« £ âì
+¢§ ¬¥­ Sprinter. …áâì ¢¥é¨ á ª®â®p묨 PC á¯p ¢¨âìáï «ãçè¥, ï í⮣® ¨ ­¥
+®âp¨æ î.
+
+          ‘ 㢠¦¥­¨¥¬, Denis.
+
+... ˆ âãâ ï ­ è¥« ­¥çâ® â ª®¥, ¨§-§  祣® áࠧ㠧 ¡ë« ¢á¥ ­ è¨ ᪫®ª¨. Ÿ
+㢨¤¥«
+---
+ * Origin: PETERS PLUS LTD (2:5030/529.48)