Rename actions folder as scripts

It's clearer this way.

.github/scripts/mingw-w64-libpng-dev.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+
+set -e
+
+pngver=1.6.37
+arch="$1"
+
+## Grab sources and check them
+
+wget http://downloads.sourceforge.net/project/libpng/libpng16/$pngver/libpng-$pngver.tar.xz
+wget http://downloads.sourceforge.net/project/apng/libpng/libpng16/libpng-$pngver-apng.patch.gz
+sha256sum -c .github/scripts/mingw-w64-libpng-dev.sha256sums
+
+## Extract sources and patch them
+
+tar -xf libpng-$pngver.tar.xz
+gunzip libpng-$pngver-apng.patch.gz
+
+# Patch in apng support
+env -C libpng-$pngver patch -p0 ../libpng-$pngver-apng.patch
+
+## Start building!
+
+mkdir -p build
+cd build
+../libpng-$pngver/configure \
+	--host="$arch" --target="$arch" \
+	--prefix="/usr/$arch" \
+	--enable-shared --disable-static \
+	CPPFLAGS="-D_FORTIFY_SOURCE=2" \
+	CFLAGS="-O2 -pipe -fno-plt -fexceptions --param=ssp-buffer-size=4" \
+	LDFLAGS="-Wl,-O1,--sort-common,--as-needed -fstack-protector"
+make -kj
+make install