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/mem_test/mem_test.c

@@ -0,0 +1,87 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <sprinter.h>
+#include <sprinter_mem.h>
+
+/*
+ * Exercises the ESTEX EMM page allocator + bank_read/bank_write helpers.
+ *
+ * Plan:
+ *  1. Show free-page count via mem_info.
+ *  2. Allocate 3 pages → block id.
+ *  3. For each page in the block, write a recognizable pattern via
+ *     bank_write, then read it back via bank_read into a near buffer.
+ *  4. Cross-check the readback to prove pages are independent.
+ *  5. Free the block, show the free-page count again.
+ */
+
+static void show_mem(const char *label)
+{
+    uint16_t total, free_pages;
+    mem_info(&total, &free_pages);
+    printf("  %s total=%u free=%u (each page = 16 KB)\n",
+           label, total, free_pages);
+}
+
+int main(void)
+{
+    puts("Sprinter page allocator demo");
+    puts("");
+
+    show_mem("before:");
+
+    uint8_t blk = mem_alloc_pages(3);
+    if (blk == 0) {
+        puts("  mem_alloc_pages(3) failed");
+        (void)getchar();
+        return 1;
+    }
+    printf("  allocated block id = %u (3 pages)\n", blk);
+    show_mem("after alloc:");
+
+    /* Show the physical page numbers we got. */
+    for (uint8_t i = 0; i < 3; i++) {
+        uint8_t phys = mem_get_page(blk, i);
+        printf("  page %u of block = phys 0x%02X\n", i, phys);
+    }
+
+    /* Write a 32-byte pattern at offset 0 of each page; pattern depends
+     * on page index so we can distinguish them. */
+    char buf[33];
+    for (uint8_t i = 0; i < 3; i++) {
+        uint8_t phys = mem_get_page(blk, i);
+        for (int j = 0; j < 32; j++) {
+            buf[j] = 'A' + (char)i;     /* page 0 -> 'A', page 1 -> 'B', page 2 -> 'C' */
+        }
+        buf[32] = 0;
+        bank_write(phys, 0, buf, 32);
+        printf("  wrote 32 x '%c' to page %u (phys 0x%02X)\n",
+               'A' + i, i, phys);
+    }
+
+    /* Read back and verify each page has its own pattern. */
+    puts("");
+    puts("readback:");
+    for (uint8_t i = 0; i < 3; i++) {
+        uint8_t phys = mem_get_page(blk, i);
+        memset(buf, 0, sizeof(buf));
+        bank_read(phys, 0, buf, 32);
+        buf[32] = 0;
+        printf("  page %u (phys 0x%02X) first 32 bytes: \"%s\"\n",
+               i, phys, buf);
+    }
+
+    /* Single-byte API spot check. */
+    bank_store_byte(mem_get_page(blk, 1), 100, 0x42);
+    uint8_t got = bank_load_byte(mem_get_page(blk, 1), 100);
+    printf("\n  store/load single byte at page1[100]: 0x%02X (expect 0x42)\n", got);
+
+    mem_free_block(blk);
+    show_mem("after free:");
+
+    puts("");
+    puts("Press any key to exit.");
+    (void)getchar();
+    return 0;
+}