Add 3D model example;

(cherry picked from commit 4271820cf0e36df8fbd8b7fd9b747c09769a7c9f)

examples/Model/conf.lua

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+function lovr.conf(t)
+  t.window.msaa = 8
+end

examples/Model/main.lua

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+function lovr.load()
+  model = lovr.graphics.newModel('duck.dae', 'duck.png')
+  lovr.graphics.setBackgroundColor(.2, .2, .2)
+end
+
+function lovr.draw()
+  model:draw(0, 0, -3, 1, 4 + lovr.timer.getTime() * .1)
+end