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/conio/conio.c

@@ -0,0 +1,128 @@
+#include <stdio.h>
+#include <conio.h>
+#include <unistd.h>     /* sleep */
+
+/*
+ * Exercises every conio function:
+ *   clrscr  — clear the screen
+ *   gotoxy  — move cursor to (x, y), 0-based
+ *   putch   — single character
+ *   cputs   — string without auto-newline
+ *   kbhit   — non-blocking key probe
+ *   getch   — blocking, no echo
+ *   getche  — blocking, with echo
+ *
+ * Sprinter native text mode is 80×32, so we anchor corners at
+ * (0,0), (79,0), (0,31), (79,31).
+ */
+
+int main(void)
+{
+    /* 1. clrscr + diagnostic probes + a centered banner.
+     *
+     * Row-0 probe: figure out why [NW]/[NE] don't paint.
+     *   '0','1','2','3' — single putch at row 0, cols 0/5/40/79
+     *   "R0"            — cputs at row 0, col 10
+     *   'a','b','c','R1'— same pattern on row 1 (control)
+     */
+    clrscr();
+
+    gotoxy(0, 0);  putch('0');
+    gotoxy(5, 0);  putch('1');
+    gotoxy(40, 0); putch('2');
+    gotoxy(79, 0); putch('3');
+    gotoxy(10, 0); cputs("R0");
+
+    gotoxy(0, 1);  putch('a');
+    gotoxy(5, 1);  putch('b');
+    gotoxy(79, 1); putch('c');
+    gotoxy(10, 1); cputs("R1");
+
+    /* Bottom corners moved to row 30 to avoid the auto-wrap-scroll issue —
+     * cputs("[SE]") at (76, 31) ends with cursor at col 80 on the last row,
+     * which scrolls the screen up by one and eats everything we wrote at
+     * row 0.  By staying on row 30, no wraparound is triggered. */
+    gotoxy(0, 30);  cputs("[SW]");
+    gotoxy(76, 30); cputs("[SE]");
+
+    /* Row 31 single-char probes (col 0 + col 78, no col-80 reach). */
+    gotoxy(0, 31);  putch('L');
+    gotoxy(78, 31); putch('R');
+
+    gotoxy(30, 4);
+    cputs("== conio test ==");
+
+    /* wherex/wherey probe — place cursor at a known spot, read it back. */
+    gotoxy(15, 5);
+    int cx = wherex();
+    int cy = wherey();
+    gotoxy(0, 6);
+    printf("wherex/wherey after gotoxy(15,5) -> x=%d y=%d", cx, cy);
+
+    /* 2. putch — single chars in a diagonal. */
+    for (int i = 0; i < 16; i++) {
+        gotoxy(10 + i, 8 + i);
+        putch('*');
+    }
+
+    /* 3. kbhit polling loop with a spinning indicator. */
+    gotoxy(0, 14);
+    cputs("kbhit polling - press any key to interrupt");
+
+    static const char spin[] = "|/-\\";
+    int frame = 0;
+    while (!kbhit()) {
+        gotoxy(50, 14);
+        putch(spin[frame & 3]);
+        frame++;
+        /* small delay so the spin is visible (sleep is in 1-sec units;
+         * we want ~10 fps — implemented with a busy "halts" later, but
+         * here we just rely on kbhit being slow enough to be visible). */
+    }
+    int probed = kbhit();   /* re-read to clear / display */
+    gotoxy(0, 16);
+    printf("kbhit captured 0x%02X ('%c')", probed,
+           (probed >= 0x20 && probed < 0x7F) ? probed : '?');
+
+    /* 4. getch — drain the key + ask for one with no echo. */
+    gotoxy(0, 18);
+    cputs("getch (no echo) — press a key: ");
+    int k1 = getch();
+    gotoxy(0, 19);
+    printf("you pressed 0x%02X ('%c')", k1,
+           (k1 >= 0x20 && k1 < 0x7F) ? k1 : '?');
+
+    /* 5. getche — same but the keypress should appear on screen. */
+    gotoxy(0, 21);
+    cputs("getche (with echo) — press a key:   ");
+    gotoxy(36, 21);
+    int k2 = getche();
+    gotoxy(0, 22);
+    printf("you pressed 0x%02X (echoed above)", k2);
+
+    /* 6. Finish at the bottom; do NOT scroll. */
+    gotoxy(0, 28);
+    cputs("All conio functions exercised. Press any key to exit.");
+    
+
+    set_videotextmode(TEXT_MODE_40x32);
+    
+    for (int i = 0; i < 16; i++) {
+        wrchar(4 + i * 2, 3, i < 10 ? '0' + i : 'A' - 10 + i, 0x1F);
+        wrchar(4 + i * 2 + 1, 3, ' ', 0x1F);
+    }
+    for (int j = 0; j < 16; j++) {
+        wrchar(2, 4 + j, j < 10 ? '0' + j : 'A' - 10 + j, 0x1F);
+        wrchar(2 + 1, 4 + j, ' ', 0x1F);
+        for (int i = 0; i < 16; i++) {
+            wrchar(4 + i * 2, 4 + j, j * 16 + i, 0x2F);
+            wrchar(4 + i * 2 + 1, 4 + j, ' ', 0x2F);
+        }
+    }
+
+    (void)getch();
+
+    set_videotextmode(TEXT_MODE_80x32);
+
+    return 0;
+}