feat(scaffold): generate a project that builds and tests unmodified

Writes a build file, a library, a binary and a test, wired so build and test
both pass immediately after init.

lib/scaffold.ml

@@ -0,0 +1,97 @@
+let build_meow name =
+  Printf.sprintf
+    {|project %s
+
+toolchain {
+  cc     cc
+  cflags -O2 -Wall -Wextra -std=c17
+}
+
+check header stdio.h
+check func sqrt in m
+check sizeof void*
+
+config_header include/%s_config.h
+
+lib %s_core {
+  srcs    src/core/*.c
+  include include
+  ldflags -lm
+}
+
+bin %s {
+  srcs    src/main.c
+  include include
+  use     %s_core
+  install bin
+}
+
+test %s_test {
+  srcs    tests/*.c
+  include include
+  use     %s_core
+}
+|}
+    name name name name name name name
+
+let core_c name =
+  Printf.sprintf
+    {|#include "%s.h"
+#include <math.h>
+
+double %s_hypot(double a, double b) { return sqrt(a * a + b * b); }
+|}
+    name name
+
+let core_h name =
+  Printf.sprintf
+    {|#ifndef %s_H
+#define %s_H
+
+double %s_hypot(double a, double b);
+
+#endif
+|}
+    (String.uppercase_ascii name) (String.uppercase_ascii name) name
+
+let main_c name =
+  Printf.sprintf
+    {|#include "%s.h"
+#include "%s_config.h"
+#include <stdio.h>
+
+int main(void) {
+    printf("%%s\n", %s_NAME);
+    printf("hypot(3,4) = %%.1f\n", %s_hypot(3.0, 4.0));
+    return 0;
+}
+|}
+    name name (String.uppercase_ascii name) name
+
+let test_c name =
+  Printf.sprintf
+    {|#include "%s.h"
+#include <math.h>
+#include <stdio.h>
+
+int main(void) {
+    if (fabs(%s_hypot(3.0, 4.0) - 5.0) > 1e-9) {
+        fprintf(stderr, "hypot is wrong\n");
+        return 1;
+    }
+    printf("ok\n");
+    return 0;
+}
+|}
+    name name
+
+let create name =
+  let w path text = if Sys.file_exists path then Diag.error "%s already exists" path else Fs.write path text in
+  w "build.meow" (build_meow name);
+  w (Printf.sprintf "include/%s.h" name) (core_h name);
+  w (Printf.sprintf "src/core/%s.c" name) (core_c name);
+  w "src/main.c" (main_c name);
+  w (Printf.sprintf "tests/%s_test.c" name) (test_c name);
+  w ".gitignore" "build/\n";
+  [ "build.meow"; "include/" ^ name ^ ".h"; "src/core/" ^ name ^ ".c"; "src/main.c";
+    "tests/" ^ name ^ "_test.c"; ".gitignore" ]