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/banked/Makefile

@@ -0,0 +1,11 @@
+# Build banked.exe — HUGE memory mode (small + banked code in W3).
+#
+# Layout:
+#   CODE/HOME at 0x4100 (W1), DATA at 0x8000 (W2), banks at 0x{N}C000 (W3).
+#   crt0_banked.s loads N banks from the .EXE before calling main.
+
+PROJ_ROOT := $(abspath $(CURDIR)/../..)
+EXAMPLE   := banked
+MEMORY    := huge
+EXTRA_FLAGS := --bank 1=bank1.c --bank 2=bank2.c
+include $(PROJ_ROOT)/examples/example.mk

examples/banked/bank1.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <sprinter.h>
+
+void bank1_func(int x) __banked
+{
+    (void)x;
+    puts("BANK1: hello from a banked function!");
+    puts("BANK1: window 3 phys page = ");
+    print_hex(_io_page_w3);     /* should be BANK1's phys page */
+    putchar('\n');
+    putchar('1');
+    putchar('=');
+    putchar('0' + (x / 10) % 10);
+    putchar('0' + x % 10);
+    putchar('\n');
+}

examples/banked/bank2.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <sprinter.h>
+
+void bank2_func(int x) __banked
+{
+    (void)x;
+    puts("BANK2: hello from the second bank!");
+    puts("BANK2: window 3 phys page = ");
+    print_hex(_io_page_w3);     /* should be BANK2's phys page */
+    putchar('\n');
+    putchar('2');
+    putchar('=');
+    putchar('0' + (x / 100) % 10);
+    putchar('0' + (x / 10) % 10);
+    putchar('0' + x % 10);
+    putchar('\n');
+}

examples/banked/banked.c

@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <sprinter.h>
+
+/* crt0_banked.s reads this constant to know how many banks to load. */
+const uint8_t n_banks = 2;
+
+void bank1_func(int x) __banked;
+void bank2_func(int x) __banked;
+
+extern uint8_t bank_pages[];   /* filled by crt0_banked.s */
+
+static void show_w3(const char *who)
+{
+    puts(who);
+    print_hex(_io_page_w3);     /* current physical page mapped in window 3 */
+    putchar('\n');
+}
+
+int main(void)
+{
+    puts("HOME: program start.");
+#ifdef DEBUG_RT
+    printf("HOME: w2_self_allocated = %u\n", w2_self_allocated);
+#endif
+    show_w3("HOME: window 3 phys page = ");
+
+    puts("HOME: bank_pages[1] (BANK1 phys) = ");
+    print_hex(bank_pages[1]);
+    putchar('\n');
+    puts("HOME: bank_pages[2] (BANK2 phys) = ");
+    print_hex(bank_pages[2]);
+    putchar('\n');
+
+    puts("HOME: calling bank1_func(42)...");
+    bank1_func(42);
+    show_w3("HOME: back, window 3 phys = ");
+
+    puts("HOME: calling bank2_func(123)...");
+    bank2_func(123);
+    show_w3("HOME: back, window 3 phys = ");
+
+    puts("HOME: done.");
+    puts("Press any key to exit...");
+    (void)getchar();
+    return 0;
+}