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>

release_docs/en/examples.md

@@ -0,0 +1,76 @@
+# Examples tour
+
+The release ships with 27 example programs in `examples/`.  Every one of them
+is a self-contained demo with comments — they were used as regression tests
+during development.
+
+## Build any example
+
+```sh
+cd examples/hello
+make
+```
+
+That produces `hello.exe` next to `hello.c` using `examples/example.mk`.
+
+## Categories
+
+### Hello world / basics
+* **`hello`** — stdio + conio Turbo-C-style colours
+* **`argv`** — argv parsing in crt0
+* **`conio`** — conio API smoke test
+* **`attrprob`** — probe Sprinter text-attribute byte layout
+
+### File I/O
+* **`cat`** — read & print TEST.TXT
+* **`seek`** — 32-bit lseek over a 100 KB file
+* **`ls`** — directory listing via ffirst/fnext
+* **`filetest`** — FILE* streams (`fopen`/`fread`/`fwrite`/`fclose`)
+* **`stattest`** — `stat`/`fstat` on files and directories
+* **`openenv`** — open() flags + environment variables
+
+### Memory & banking
+* **`malloc`** — heap stress test (200+ allocations)
+* **`mem_test`** — page allocator + `bank_read`/`bank_write`
+* **`banked`** — banked code in W3 (huge mode)
+* **`bankedbg`** — banked code in W1 (big mode)
+* **`banklocl`** — bank-local static data and BSS
+
+### Mouse
+* **`mouse`** — driver in text mode
+* **`gfx_mous`** — mouse with custom bitmap cursor in graphics mode
+
+### Graphics
+* **`gfx_demo`** — 320×256×256: lines, rectangles, fill via accelerator
+* **`gfx_d16`** — 640×256×16: same primitives in 16-color mode
+* **`gfx_text`** — bitmap-font text on graphics screen
+
+### Misc
+* **`errno`** — errno / strerror / perror
+* **`timedir`** — date/time + directory listing
+* **`ptime`** — POSIX time API (time / localtime / mktime)
+* **`strtest`** — `<string.h>` test (from SDCC's z80.lib)
+* **`stdlib`** — `<stdlib.h>` test (qsort / rand / strtol / etc.)
+* **`assrtest`** — assert()
+* **`rt_test`** — runtime helpers (sleep, setjmp, atexit)
+
+## Example.mk
+
+Every example uses `examples/example.mk`.  A minimal Makefile looks like:
+
+```makefile
+PROJ_ROOT := $(abspath $(CURDIR)/../..)
+EXAMPLE   := my_app
+include $(PROJ_ROOT)/examples/example.mk
+```
+
+Optional knobs (set before `include`):
+
+```makefile
+MEMORY      := huge                       # default tiny
+STACK_SIZE  := 4096                       # default ~1278
+EXTRA_SRCS  := helper.c util.c            # extra .c files in same dir
+EXTRA_FLAGS := --bank 1=engine.c --debug  # pass-through to sprinter-cc
+```
+
+Use this template for your own programs.