Adapt C++ examples to recent changes in appleseed#2751

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Mango-3 wants to merge 3 commits intoappleseedhq:masterfrom Mango-3:examplefix

+36-16

Commits on Dec 24, 2019

Change fixed width integer types to C++11 std
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Commits on Dec 25, 2019

Add override of virtual function to derived class
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Commits on Dec 27, 2019

Review fixes 1
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