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/SPRN2K47.TXT

@@ -0,0 +1,45 @@
+*** Area: ZX.SPECTRUM                             Date: 27 Apr 01  2:54:35
+*** From: Ivan Mak (2:5030/529.24)
+*** To  : Eugene Ostroukhov
+*** Subj: ˆ­ä 
+
+
+        �ਢ¥âáâ¢ãî ‚ á, Eugene!
+
+  <Thursday April 26 2001> <11:24> Eugene Ostroukhov wr®te to Ivan Mak:
+
+ >>  EO> WarcraftII/Doom.
+ >>     ^^^^^^^^^^^^^^^^^^
+ >>  EO> �ਧ­ ©, çâ® á ¬ë¥ á®¢à¥¬¥­­ë¥ ¯à®£¨ ­  ‘¯à¨­â¥à¥ ­¥
+ >>  EO> ᬮ£ãâ ®¡¥á¯¥ç¨âì  ­ «®£¨ç­ëå ¢®§¬®¦­®á⥩... :(
+ >>
+ >> �®¤ç¥pª­ã⮥ - ­¥ ¯p¨§­ î. �â® ¢®§¬®¦­®, ¨ ¤ ¦¥ ¡®«¥¥...
+
+ EO> 320x200x256 - Doom
+
+H  Sprinter-¥ ¥áâì 3d-demo 320x256x256 25/17 frames/sec, á ¬ã§ëª «ì­ë¬
+ᮯp®¢®¦¤¥­¨¥¬ ­  COVOX-Blaster-¥ (¨£p ¥â ¬ã§ëªã á HDD), ¨ á è㬮¢ë¬¨
+íä䥪⠬¨ ¯p¨ ¢ëáâp¥« å ¯® ¬®­áâp ¬...
+
+_�⮠㦥 ¥áâì ­  Sp97_
+
+ EO> 640x480x256 - Warcraft II. ˆ í⮠⮫쪮 £à ä¨ª .
+
+ƒp ä¨ª  ­  ‘¯p¨­â¥p¥ ᥩç á ¢®§¬®¦­  ¤® 640x256x16.
+�㤥⠢ ¡«¨¦ ©è¥¥ ¢p¥¬ï 640x256x256. —¨á«® áâp®ª ®£p ­¨ç¨¢ ¥âáï ⥫¥¢¨§®p®¬.
+€ªá¥«¥p â®p ¯®§¢®«ï¥â ¢ë¢®¤¨â á¯p ©âë ¤®áâ â®ç­® ¡ëáâp®, â ª çâ®
+­¥çâ® ¯®¤®¡­®¥ WarCraft ¢¯®«­¥ ¢®§¬®¦­®.
+’¥¬ ¡®«¥¥ ¤«ï ­¥£® ¤ ¦¥ 17/12 FPS ­®p¬ «ì­®...
+
+ EO> ’®â Doom, çâ® ï ¢¨¬¤¥« ­  ‘¯¥ª¨ (¤¥¬ , ¯®¤ í¬ã«¥¬) ¤ «¥ª ®â
+ EO> �–è­®£®...
+
+’®â Doom, çâ® ¤«ï Spectrum- , ®ç¥­ì ¤ «¥ª ®â ⮣®, ç⮠㦥 ¥áâì ­  Sprinter-¥.
+
+        �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)