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/timedir/Makefile

@@ -0,0 +1,5 @@
+# Build time_dir_test.exe — uses lib/sprinter.lib in TINY memory mode.
+
+PROJ_ROOT := $(abspath $(CURDIR)/../..)
+EXAMPLE   := timedir
+include $(PROJ_ROOT)/examples/example.mk

examples/timedir/timedir.c

@@ -0,0 +1,108 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <time.h>
+#include <errno.h>
+#include <string.h>
+#include <conio.h>
+
+static const char *dow_name(uint8_t d)
+{
+    /* Sprinter SYSTIME returns dow 1-based: 1=Sun..7=Sat. */
+    static const char *names[] = { "?", "Sun", "Mon", "Tue",
+                                   "Wed", "Thu", "Fri", "Sat" };
+    return (d >= 1 && d <= 7) ? names[d] : names[0];
+}
+
+int main(void)
+{
+    /* --- time ----------------------------------------------------------- */
+    datetime_t dt;
+    getdatetime(&dt);
+    printf("getdatetime: %04u-%02u-%02u %02u:%02u:%02u (dow=%u %s)\n",
+           dt.year, dt.month, dt.day,
+           dt.hour, dt.minute, dt.second,
+           dt.dow, dow_name(dt.dow));
+
+    /* dow convention probe — set to known dates, read back.
+     * Discriminating test: today (Thu) gave dow=5, which fits either
+     *   (a) Sun=1, Mon=2, ..., Sat=7   (DOS 1-based starting Sun)
+     *   (b) Sat=0, Sun=1, ..., Fri=6   (week starts Saturday)
+     * Saturday's number tells us which one. */
+    datetime_t saved = dt;
+    datetime_t probe;
+
+    probe = dt; probe.year = 2026; probe.month = 5; probe.day = 30;  /* Sat */
+    if (setdatetime(&probe) == 0) {
+        getdatetime(&probe);
+        printf("probe 2026-05-30 (Sat expected): dow=%u %s\n",
+               probe.dow, dow_name(probe.dow));
+    }
+
+    probe = dt; probe.year = 2026; probe.month = 5; probe.day = 31;  /* Sun */
+    if (setdatetime(&probe) == 0) {
+        getdatetime(&probe);
+        printf("probe 2026-05-31 (Sun expected): dow=%u %s\n",
+               probe.dow, dow_name(probe.dow));
+    }
+
+    probe = dt; probe.year = 2026; probe.month = 6; probe.day = 1;   /* Mon */
+    if (setdatetime(&probe) == 0) {
+        getdatetime(&probe);
+        printf("probe 2026-06-01 (Mon expected): dow=%u %s\n",
+               probe.dow, dow_name(probe.dow));
+    }
+
+    /* Restore original. */
+    if (setdatetime(&saved) == 0)
+        printf("restored original date\n");
+    else
+        printf("setdatetime(restore) failed: errno=%d\n", errno);
+
+    /* --- getcwd --------------------------------------------------------- */
+    char cwd[256];
+    if (getcwd(cwd, sizeof cwd) == NULL) {
+        printf("getcwd failed: errno=%d (%s)\n", errno, strerror(errno));
+    } else {
+        printf("cwd before:  \"%s\"\n", cwd);
+    }
+
+    /* --- mkdir / chdir / getcwd / rmdir --------------------------------- */
+    const char *test_dir = "TMPTEST";
+
+    /* If a previous run left it behind, ignore the mkdir failure. */
+    if (mkdir(test_dir) < 0) {
+        printf("mkdir(%s) -> errno=%d (%s) [continuing]\n",
+               test_dir, errno, strerror(errno));
+    } else {
+        printf("mkdir(%s) OK\n", test_dir);
+    }
+
+    if (chdir(test_dir) < 0) {
+        printf("chdir(%s) failed: errno=%d (%s)\n",
+               test_dir, errno, strerror(errno));
+        return 1;
+    }
+    printf("chdir(%s) OK\n", test_dir);
+
+    if (getcwd(cwd, sizeof cwd) != NULL)
+        printf("cwd after:   \"%s\"\n", cwd);
+
+    /* Back out, then remove. */
+    if (chdir("\\") < 0)
+        printf("chdir(\\) failed: errno=%d\n", errno);
+    else
+        printf("chdir(\\) OK\n");
+
+    if (rmdir(test_dir) < 0)
+        printf("rmdir(%s) failed: errno=%d (%s)\n",
+               test_dir, errno, strerror(errno));
+    else
+        printf("rmdir(%s) OK\n", test_dir);
+
+    if (getcwd(cwd, sizeof cwd) != NULL)
+        printf("cwd final:   \"%s\"\n", cwd);
+
+    puts("\npress any key to exit");
+    (void)getch();
+    return 0;
+}