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/SPRN2K02.TXT

@@ -0,0 +1,75 @@
+*** Area: ZX.SPECTRUM                             Date: 18 Mar 01 11:50:05
+*** From: Ivan Mak (2:5030/529.24)
+*** To  : Stanislav Udin
+*** Subj: Ž ‘¯p¨­â¥p¥.
+
+
+        �ਢ¥âáâ¢ãî ‚ á, Stanislav!
+
+  <Tuesday March 13 2001> <15:11> Stanislav Udin wr®te to Ivan Mak:
+
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+­ ¯®¤®¡¨¥ ®¡­ p㦥­¨ï ªp㯭ëå £«îª®¢ ¢ ¯« â¥....
+
+ SU>>> Œ®¦­® «¨ ­ áâp®¨âì ‘¯p¨­â¥p â ª, çâ®¡ë ¢ª«î稢 ¥£® ¤ ¦¥ ¨ ­¥
+ SU>>> ¯®¤®§p¥¢ âì, çâ® p ¡®â ¥èì ­¥ ­  ‘ª®p¯¨®­¥?
+ IM>> ’ ª çâ® ¡ë ᮢᥬ ­¥ ¯®¤®§p¥¢ âì, ­¥ ¯®«yç¨âáï :-)
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+ SU> ª®¬¯ìîâ¥p ¨ ...
+
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+ IM>> H ¤¥îáì, ¯p®¡«¥¬ ­¥ ¡y¤¥â.
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+
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+Hã ¨ ¥é¥ ª­®¯ª  Power :)
+
+ SU> € ¬­®£® «¨ ¢®®¡é¥ ¯®«ì§®¢ â¥«¥© ‘¯p¨­â¥p ? Œ­®£® «¨ ¨§ ­¨å ¯¨èyâ �Ž
+ SU> ¤«ï ¤®¯®«­¨â¥«ì­ëå p¥¦¨¬®¢ í⮣® ª®¬¯ìîâ¥p ?
+
+�®«ì§®¢ â¥«¥© ¯p¨¬¥p­® 25, â®ç­¥¥ ᥩç á ­¥ §­ î.
+ˆ§ ¯¨èãé¨å �Ž â®ç­® ¥áâì ¤¢®¥ (ï ­¥ ¢ áç¥â),   ¯® á«ãå ¬
+ªâ®-â® ¥é¥ ⮦¥ § ­¨¬ ¥âáï ¯p®£p ¬¬ ¬¨...
+
+        �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)