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/strtest/Makefile

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

examples/strtest/strtest.c

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <string.h>
+
+static void check(const char *label, int ok)
+{
+    puts(label);
+    puts(ok ? "  OK" : "  FAIL");
+}
+
+int main(void)
+{
+    char buf[32];
+
+    /* strlen */
+    check("strlen(\"\") == 0",         strlen("") == 0);
+    check("strlen(\"hello\") == 5",    strlen("hello") == 5);
+
+    /* strcpy + strlen */
+    strcpy(buf, "Sprinter");
+    check("strcpy + strlen == 8",      strlen(buf) == 8);
+
+    /* strcmp */
+    check("strcmp(\"a\",\"a\") == 0",  strcmp("a", "a") == 0);
+    check("strcmp(\"a\",\"b\") < 0",   strcmp("a", "b") < 0);
+    check("strcmp(\"b\",\"a\") > 0",   strcmp("b", "a") > 0);
+    check("strcmp(buf,\"Sprinter\")",  strcmp(buf, "Sprinter") == 0);
+
+    /* strcat */
+    strcpy(buf, "Hello ");
+    strcat(buf, "Sprinter!");
+    check("strcat -> \"Hello Sprinter!\"", strcmp(buf, "Hello Sprinter!") == 0);
+
+    /* memcpy */
+    memset(buf, 'X', 16);
+    memcpy(buf + 4, "ABCD", 4);
+    buf[16] = 0;
+    check("memset+memcpy -> \"XXXXABCDXXXXXXXX\"",
+          strcmp(buf, "XXXXABCDXXXXXXXX") == 0);
+
+    /* memset */
+    memset(buf, 'q', 5);
+    buf[5] = 0;
+    check("memset(buf,'q',5) -> \"qqqqq\"", strcmp(buf, "qqqqq") == 0);
+
+    /* memcmp */
+    check("memcmp equal",   memcmp("abcd", "abcd", 4) == 0);
+    check("memcmp diff",    memcmp("abcd", "abxd", 4) != 0);
+
+    puts("");
+    puts("All checks done.  Press any key to exit.");
+    (void)getchar();
+    return 0;
+}