feat(examples): add a hello project with a library and a consumer

Smallest project that exercises the whole pipeline: one static library and one
executable that links against it.

examples/hello/build.meow

@@ -0,0 +1,19 @@
+project hello
+
+toolchain {
+  cc      clang
+  cflags  -O2 -Wall -Wextra -std=c17
+}
+
+lib mathx {
+  srcs    src/mathx/*.c
+  include include
+  ldflags -lm
+}
+
+bin hello {
+  srcs    src/main.c
+  include include
+  use     mathx
+  define  GREETING="meow"
+}

examples/hello/include/mathx.h

@@ -0,0 +1,12 @@
+#ifndef MATHX_H
+#define MATHX_H
+
+#include <stddef.h>
+
+double vec_dot(const double *a, const double *b, size_t n);
+double vec_norm(const double *a, size_t n);
+double vec_sum(const double *a, size_t n);
+double stats_mean(const double *a, size_t n);
+double stats_stddev(const double *a, size_t n);
+
+#endif

examples/hello/src/main.c

@@ -0,0 +1,18 @@
+#include "mathx.h"
+#include <stdio.h>
+
+#ifndef GREETING
+#define GREETING "hello"
+#endif
+
+int main(void) {
+    double xs[] = {1.0, 2.0, 3.0, 4.0, 5.0};
+    size_t n = sizeof xs / sizeof xs[0];
+
+    printf("%s\n", GREETING);
+    printf("  dot    %.3f\n", vec_dot(xs, xs, n));
+    printf("  norm   %.3f\n", vec_norm(xs, n));
+    printf("  mean   %.3f\n", stats_mean(xs, n));
+    printf("  stddev %.3f\n", stats_stddev(xs, n));
+    return 0;
+}

examples/hello/src/mathx/vec.c

@@ -0,0 +1,16 @@
+#include "mathx.h"
+#include <math.h>
+
+double vec_dot(const double *a, const double *b, size_t n) {
+    double sum = 0.0;
+    for (size_t i = 0; i < n; i++) sum += a[i] * b[i];
+    return sum;
+}
+
+double vec_norm(const double *a, size_t n) { return sqrt(vec_dot(a, a, n)); }
+
+double vec_sum(const double *a, size_t n) {
+    double s = 0.0;
+    for (size_t i = 0; i < n; i++) s += a[i];
+    return s;
+}