Compiler and docs on every system: macOS Intel in CI, releases made by CI, docs for vectors and --cpu

- CI: macOS on Apple Silicon and Intel (macos-15, macos-15-intel); a tag v* attaches every package
  (Linux x64/ARM64, macOS ARM64/x64, Windows x64, the VS Code extension) to its release
- vectors: fma is llvm.fmuladd (llvm.fma was a libm call per lane without FMA hardware: 3.5x slower)
- examples/simd.fch: a dot product eight at a time, timed against the plain loop
- README and the English guides: installing on Linux, macOS and Windows; vectors (SIMD); --cpu;
  -g is DWARF on Windows too (lldb from llvm-mingw); no more mention of the C++ compiler
- comments left from the C++ compiler (src/target.cpp, src/codegen.cpp, "never frees") brought up to date

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Psc42moPLwP43Cmb9oZqSR

examples/simd.fch

@@ -0,0 +1,69 @@
+// Vectors (SIMD): eight f32 at once instead of one.
+//
+//   finch run examples/simd.fch                 runs on any x86-64 or ARM64 processor
+//   finch run examples/simd.fch --cpu native    uses all of this one's instructions (AVX2, AVX-512, NEON)
+import time
+
+// one number at a time
+fn dot_plain([]f32 a, []f32 b) -> f32 {
+    f32 total = 0.0
+    for i in 0..a.len {
+        total += a[i] * b[i]
+    }
+    return total
+}
+
+// eight at a time: f32x8(list, i) takes list[i] ... list[i+7], fma multiplies and adds in one step
+fn dot_simd([]f32 a, []f32 b) -> f32 {
+    acc := f32x8(0.0)
+    i := 0
+    while i + 8 <= a.len {
+        acc = f32x8(a, i).fma(f32x8(b, i), acc)
+        i += 8
+    }
+    total := acc.sum()
+    while i < a.len {                   // the few that are left
+        total += a[i] * b[i]
+        i += 1
+    }
+    return total
+}
+
+// brighten every color: the same work on every lane, with min keeping it below 1
+fn brighten([]f32 pixels, f32 amount) {
+    i := 0
+    while i + 8 <= pixels.len {
+        v := min(f32x8(pixels, i) * (1.0 + amount), 1.0)
+        v.store(pixels, i)
+        i += 8
+    }
+}
+
+fn main() {
+    []f32 a
+    []f32 b
+    for i in 0..4_000_000 {
+        a.push(f32(i % 100) / 100.0)
+        b.push(0.5)
+    }
+
+    start := time.millis()
+    x := 0.0
+    for round in 0..20 {
+        x = float(dot_plain(a, b))
+    }
+    plain := time.millis() - start
+
+    start = time.millis()
+    y := 0.0
+    for round in 0..20 {
+        y = float(dot_simd(a, b))
+    }
+    simd := time.millis() - start
+
+    print("one at a time: ", str(x, 1), "in", plain, "ms")
+    print("eight at a time:", str(y, 1), "in", simd, "ms")
+
+    brighten(a, 0.5)
+    print("brightened:", a[10], a[90], a.len)
+}