Improve Middleware documentation and compile time static assertions#864

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Guiorgy wants to merge 3 commits intoCrowCpp:masterfrom

Guiorgy:middleware

Commits on Aug 6, 2024

added contains_decayed to black_magic
Guiorgy
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added is_superset_of to black_magic
Guiorgy
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statically assert that template types passed to Crow are a subset of the types of the arguments passed to the constructor
Guiorgy
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