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/SPRN2K20.TXT

@@ -0,0 +1,55 @@
+*** Area: ZX.SPECTRUM                             Date:  6 Apr 01  3:40:49
+*** From: Slavka Kalinin (2:5030/885.50)
+*** To  : Dmitry Ishankulov
+*** Subj: ‘¯à¨­â¥à ¨ â.¯.
+
+
+
+ƒ¤¥-â®  04-04-01 ®ª®«® 16:16:19
+Dmitry Ishankulov ­ áâãç « ­  ª« ¢¥ ­¥ª®¬ã All,
+¯à® ‘¯à¨­â¥à ¨ â.¯. ...
+
+
+
+ DI> ‡¤à áâ¢ã©, All!
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+®¤¨­ 祫®¢¥ª
+ DI> ­¥ § å®ç¥â ¯p®¬¥­ïâì ᢮© Pentium ¨«¨ Mac ­  ‘¯p¨­â¥p.
+ DI> Š ¦¤ë© ¯®«ì§®¢ â¥«ì ¡ã¤¥â p áᬠâp¨¢ âì á ¡¦¥¢ë© ª®¬ ª ª ¤®¯®«­¥­¨¥ ª
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+ˆ­â¥p­¥â,ᬮâpî
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+ª®¬¯ìîâ¥à­®¥ ¨§¤ ­¨¥ ¯®¤ ­ §¢ ­¨¥¬ ZX-News ¤¥« ¥âáï ­ 
+‘¯à¨­â¥à¥.
+
+ DI> „® ᢨ¤ ­¨ï!
+
+ DI> -+- Traffic Increaser 3.0.1
+ DI>  + Origin: With Love From Russia ishankulov@mail.ru (2:5010/50.25)
+
+   H  í⮬ ãá¥. �®ª , Dmitry!
+
+[CGE] [ARTVIEW] [THE KNIGHT'S ARENA] [IF GAME]
+to be continued ...
+
+NEWART/n-Discovery * Coder, gfx artist, AY music's fanat
+
+--- DME v1.23+Ay rulez foreva
+ * Origin: ZX Spectrum of the best hobby  (2:5030/885.50)