finalize schema/data setup

Signed-off-by: Folling <mail@folling.io>

docs/Flags.md

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+All mutating functions take a flag argument that can be used to control the behavior of the function. The flags are
+defined in a corresponding enum. The flags are passed as a bitset, so multiple flags can be passed at once by using the
+bitwise OR operator `|`.
+
+The reason for this feature is ABI stability.

docs/Ownership.md

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+### Getters
+
+Returned data remains owned by libikarus, the exception are Entity(Property)Values.
+
+### Setters
+
+libikarus assumes ownership of any data passed into it, the exception are Entity(Property)Values.

docs/internal/Caching.md

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+libikarus doesn't perform any caching as the filesystem & SQLite already cache quite well.
+Until we can see that there's a performance overhead no caching will be implemented.