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>

examples/example.mk

@@ -0,0 +1,76 @@
+# example.mk — shared Makefile fragment for simple Sprinter ESTEX examples.
+#
+# Usage in an example's Makefile:
+#
+#   PROJ_ROOT := $(abspath $(CURDIR)/../..)
+#   EXAMPLE   := my_example          # base name (matches my_example.c)
+#
+#   # Optional overrides (any combination):
+#   # MEMORY     := small             # tiny | small | big | huge | manual
+#   # STACK_SIZE := 2048              # bytes reserved for the stack
+#   # EXTRA_SRCS := helper.c util.c   # additional .c files in this dir
+#   # EXTRA_FLAGS := --crt0=minimal   # passed through to sprinter-cc
+#   # EXTRA_DATA := test.txt          # extra files to add to `make floppy`
+#
+#   include $(PROJ_ROOT)/examples/example.mk
+#
+# Pipeline (all driven by sprinter-cc):
+#   crt0 + EXAMPLE.c + EXTRA_SRCS  --sdcc-->  .ihx
+#   .ihx                            --mkexe--> EXAMPLE.exe
+# linking against lib/sprinter.lib for libc.
+#
+# Targets provided:
+#   all      build $(EXAMPLE).exe                                   (default)
+#   clean    remove build artefacts
+#   floppy   build the example and pack it (alone, plus EXTRA_DATA) into
+#            mame/v306/IMG/mc.img — useful for trying a single program
+#            without rebuilding every example.  Top-level `make floppy`
+#            (in the repo root) still packs all examples.
+#   run      floppy + launch MAME
+
+SPRINTER_CC := $(PROJ_ROOT)/bin/sprinter-cc
+MKEXE       := $(PROJ_ROOT)/toolchain/mkexe/mkexe
+LIB         := $(PROJ_ROOT)/lib/sprinter.lib
+
+MAME_DIR    := $(PROJ_ROOT)/mame/v306
+FLOPPY_IMG  := $(MAME_DIR)/IMG/mc.img
+MAKE_DISK   := $(MAME_DIR)/make_disk.py
+RUN_MAME    := $(MAME_DIR)/run_mame.sh
+
+# Optional knobs — see top of file.
+MEMORY      ?= tiny
+SOURCES     := $(EXAMPLE).c $(EXTRA_SRCS)
+
+CC_FLAGS    := --memory $(MEMORY)
+ifneq ($(STACK_SIZE),)
+CC_FLAGS    += --stack-size $(STACK_SIZE)
+endif
+CC_FLAGS    += $(EXTRA_FLAGS)
+
+all: $(EXAMPLE).exe
+
+$(EXAMPLE).exe: $(SOURCES) $(MKEXE) $(LIB)
+	$(SPRINTER_CC) $(CC_FLAGS) -o $@ $(SOURCES)
+
+$(MKEXE):
+	$(MAKE) -C $(PROJ_ROOT)/toolchain/mkexe
+
+$(LIB):
+	$(MAKE) -C $(PROJ_ROOT)/lib
+
+clean:
+	rm -rf .sprinter-cc-* $(EXAMPLE).exe
+
+# `make floppy` packs ONLY this example (+ optional EXTRA_DATA files) into
+# the MAME floppy image, replacing whatever was there.  Handy for trying a
+# single program without rebuilding all 27 examples.
+floppy: $(EXAMPLE).exe
+	python3 $(MAKE_DISK) $(FLOPPY_IMG) $(EXAMPLE).exe $(EXTRA_DATA)
+	@echo
+	@echo "Floppy ready: $(FLOPPY_IMG) (with $(EXAMPLE).exe$(if $(EXTRA_DATA), + $(EXTRA_DATA))) "
+	@echo "Run:  cd $(MAME_DIR) && ./run_mame.sh"
+
+run: floppy
+	cd $(MAME_DIR) && ./run_mame.sh
+
+.PHONY: all clean floppy run