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/samples/edit_sor/README.TXT

@@ -0,0 +1,19 @@
+Sources of sample text editor for Sprinter computer.
+Free for usage.
+
+This is example of programming for the 640x256 graphic mode of Sprinter computer.
+It need Asm80Win cross-assembler. You will found it in this archive.
+
+Also, archive include already compiled program 'ed.exe' for Sprinter computer.
+
+Compiling your variant of editor.
+Create directory 'C:\speccy\aedit\' and put archive contents in it.
+Execute Asm80Win.exe and input name of 'editor.a80' file.
+Then rename 'editor.bin' file to 'editor.exe' file and execute this new program on Sprinter computer.
+
+If you have any questions, ask us at the webforum: www.forum.petersplus.ru
+
+
+---
+Sprinter Team.
+