Add experimental alpine linux64 base image

variants/windows-install-shared.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+package_variant() {
+    IN="$1"
+    OUT="$2"
+
+    mkdir -p "$OUT"/bin
+    cp "$IN"/bin/*.{exe,dll} "$OUT"/bin
+
+    mkdir -p "$OUT"/lib
+    cp "$IN"/bin/*.lib "$OUT"/lib
+    cp "$IN"/lib/*.{def,dll.a} "$OUT"/lib
+
+    mkdir -p "$OUT"/include
+    cp -r "$IN"/include/* "$OUT"/include
+
+    mkdir -p "$OUT"/doc
+    cp -r "$IN"/share/doc/ffmpeg/* "$OUT"/doc
+}