sceneconverter: add .gitattributes and conversion script for test files.

Because no way I'm doing that conversion and diffing by hand every time.

src/Magnum/SceneTools/Test/SceneConverterTestFiles/.gitattributes

@@ -0,0 +1,11 @@
+# You have to add the following to your .git/config or global
+# ~/.gitconfig to make the binary diffs work (without the comment
+# character, of course):
+#
+# [diff "hex"]
+#     textconv = hexdump -v -C
+#     binary = true
+#
+
+*.bin binary diff=hex
+*.ply binary diff=hex

src/Magnum/SceneTools/Test/SceneConverterTestFiles/convert.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+set -e
+
+# in -> bin
+for i in *.bin.in; do
+    ../../../../../../magnum-plugins/src/MagnumPlugins/GltfImporter/Test/in2bin.py ${i}
+done

src/Magnum/SceneTools/Test/SceneConverterTestFiles/two-triangles-transformed.bin.in

@@ -1,6 +1,4 @@
-# Like two-triangles.obj, but the second triangle moved 10 units on Y. Convert
+# Like two-triangles.obj, but the second triangle moved 10 units on Y
-# with magnum-plugins/src/MagnumPlugins/GltfImporter/Test/in2bin.py.
-
 type = "3f3f3f 3f3f3f"
 input = [
     -1,  1, 0,