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/filetest/filetest.c

@@ -0,0 +1,74 @@
+/*
+ * filetest — exercise minimal FILE * stream API (fopen/fclose/fputs/
+ * fgets/fread/fwrite/fseek/ftell/feof + stdin/stdout/stderr).
+ *
+ * Steps:
+ *   1. fopen("FILE.TXT","w"), fputs+fputc lines, fclose.
+ *   2. fopen("FILE.TXT","r"), fgets each line, fclose.
+ *   3. fopen("r"), fread block, fseek, ftell, feof, fread again.
+ *   4. fputs to stdout (sanity check console pseudo-stream).
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+
+int main(void)
+{
+    const char *path = "FILE.TXT";
+
+    /* ----- 1. Write via fputs + fputc ----- */
+    {
+        FILE *fp = fopen(path, "w");
+        if (!fp) {
+            printf("fopen(w) failed: errno=%d (%s)\n", errno, strerror(errno));
+            return 1;
+        }
+        fputs("Hello from FILE*\n", fp);
+        fputs("Second line via fputs\n", fp);
+        for (int i = '0'; i <= '9'; i++) fputc(i, fp);
+        fputc('\n', fp);
+        if (fclose(fp) != 0) puts("fclose: error");
+    }
+
+    /* ----- 2. Read via fgets ----- */
+    {
+        FILE *fp = fopen(path, "r");
+        if (!fp) {
+            printf("fopen(r) failed: errno=%d\n", errno);
+            return 1;
+        }
+        char buf[128];
+        int n = 0;
+        while (fgets(buf, sizeof buf, fp)) {
+            printf("  line %d: %s", ++n, buf);
+            if (buf[strlen(buf)-1] != '\n') putchar('\n');
+        }
+        printf("  total lines: %d, feof=%d\n", n, feof(fp));
+        fclose(fp);
+    }
+
+    /* ----- 3. fread / fseek / ftell ----- */
+    {
+        FILE *fp = fopen(path, "r");
+        if (!fp) return 1;
+        char buf[16];
+        size_t got = fread(buf, 1, 16, fp);
+        printf("  fread(16) -> %u bytes, ftell=%ld\n",
+               (unsigned)got, ftell(fp));
+        if (fseek(fp, 0L, SEEK_END) == 0) {
+            printf("  file size via fseek(END)+ftell = %ld\n", ftell(fp));
+        }
+        rewind(fp);
+        printf("  rewind: ftell=%ld, feof=%d\n", ftell(fp), feof(fp));
+        fclose(fp);
+    }
+
+    /* ----- 4. Console pseudo-streams ----- */
+    fputs("  fputs to stdout works\n", stdout);
+    fputs("  fputs to stderr works\n", stderr);
+    fputc('!', stdout); fputc('\n', stdout);
+
+    puts("filetest done.");
+    return 0;
+}