Add 'xo-expression/' from commit '5ac3c03a0c'

git-subtree-dir: xo-expression
git-subtree-mainline: d0f5ccc1ce
git-subtree-split: 5ac3c03a0c

xo-expression/LESSONS

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+* want reflection to work without requiring std::type_info,
+  so that in xo-expression we can create function types that
+  C++ compiler has never encountered.
+
+** This means we need the ability to construct the canonical name
+   for a type without c++ compiler's assistance.
+
+** need lookup using function ingredients (return types + arg types + noexcept)
+   to intern lambda types