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>

lib/Makefile

@@ -0,0 +1,80 @@
+# Build lib/libsprinter.lib — the Sprinter target libc archive.
+#
+# Includes all libc/*.c modules plus the runtime helpers that get
+# auto-pulled by SDCC's codegen (heap for malloc, bank trampolines for
+# __banked).  The crt0 family is NOT in the lib — they are always
+# explicitly linked, never DCE-eligible.
+#
+# Each .c file becomes its own .rel inside the archive.  The linker
+# pulls only those .rel files whose exported symbols are referenced,
+# giving free dead-code elimination at module granularity.
+
+PROJ_ROOT := $(abspath $(CURDIR)/..)
+SDCC_BIN  := $(PROJ_ROOT)/third_party/sdcc/bin
+SDCC      := $(SDCC_BIN)/sdcc
+SDAR      := $(SDCC_BIN)/sdar
+SDASZ80   := $(SDCC_BIN)/sdasz80
+
+INC       := -I$(PROJ_ROOT)/libc/include
+CC_FLAGS  := -mz80 --no-std-crt0 --std-c99 --opt-code-size $(INC)
+
+BUILD     := $(PROJ_ROOT)/lib/build
+
+# All libc C modules.
+LIBC_C := \
+    libc/io/atexit.c   libc/io/conio.c    libc/io/cprintf.c  libc/io/dir.c \
+    libc/io/videomode_raw.c \
+    libc/io/_errno_set.c \
+    libc/io/env.c      libc/io/errno.c    libc/io/fsdir.c \
+    libc/io/lseek.c    libc/io/mouse.c    libc/io/open.c \
+    libc/io/read.c     libc/io/sleep.c \
+    libc/io/time.c     libc/io/posix_time.c  libc/io/unlink.c \
+    libc/io/stat.c \
+    libc/mem/bank_io.c libc/mem/mem_alloc.c \
+    libc/gfx/gfx_core.c       libc/gfx/gfx_raw_common.c \
+    libc/gfx/gfx_raw_256.c    libc/gfx/gfx_raw_16.c \
+    libc/gfx/gfx_256.c        libc/gfx/gfx_16.c \
+    libc/gfx/gfx_font.c       libc/gfx/gfx_text_256.c \
+    libc/gfx/gfx_text_16.c \
+    libc/stdio/getchar.c libc/stdio/print_hex.c \
+    libc/stdio/putchar.c libc/stdio/puts.c libc/stdio/file.c \
+    libc/stdio/solid_helpers.c libc/io/solid_compat.c
+
+# Runtime modules to bundle (pulled by symbol references from libc-using code).
+# NOTE: runtime/bank.s is NOT bundled — its trampoline depends on the banking
+# window (W1 for BIG, W3 for HUGE) which is decided per-build by sprinter-cc.
+# That tool assembles bank.s on each banked build with the right BANK_W1 flag.
+RUNTIME_S := runtime/heap.s
+
+LIBC_RELS    := $(patsubst libc/%.c,$(BUILD)/%.rel,$(LIBC_C))
+RUNTIME_RELS := $(patsubst runtime/%.s,$(BUILD)/%.rel,$(RUNTIME_S))
+
+ALL_RELS := $(LIBC_RELS) $(RUNTIME_RELS)
+
+LIB := sprinter.lib
+
+all: $(LIB)
+
+# Pattern rule for C modules — preserves the libc/io|mem|stdio path
+# so .rel members keep their natural names inside the archive.
+$(BUILD)/%.rel: $(PROJ_ROOT)/libc/%.c
+	@mkdir -p $(dir $@)
+	$(SDCC) $(CC_FLAGS) -c -o $@ $<
+
+# Runtime .s → .rel
+$(BUILD)/%.rel: $(PROJ_ROOT)/runtime/%.s
+	@mkdir -p $(dir $@)
+	$(SDASZ80) -o $@ $<
+
+# Archive — sdar with `rcs` = replace/create/symtab.
+$(LIB): $(ALL_RELS)
+	rm -f $@
+	$(SDAR) -rcs $@ $(ALL_RELS)
+	@echo
+	@echo "  Built $@ with $(words $(ALL_RELS)) modules:"
+	@$(SDAR) -t $@ | sed 's/^/    /'
+
+clean:
+	rm -rf $(BUILD) $(LIB)
+
+.PHONY: all clean