Fix #224: static_assert is_sorted().

[Stephan T. Lavavej (StephanTLavavej)]

Description

Now that #6 has been implemented, we can fix #224 by static_asserting is_sorted() for lookup tables. This guarantees safety with zero runtime cost.

Checklist

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[Stephan T. Lavavej (StephanTLavavej)]

I filed #455 to track the fact that we can't change validate.cpp yet (the tools don't use the freshly-built STL, d'oh).