elemsof should be renamed as countof

[chqrlie]

countof is already used in many existing packages in C, C++ and other languages, while elemsof seems unique to C2.

The Standard C Committee has approved the addition of _Countof in the next version of the C Standard. A survey was conducted to determine the best choice of word for the operator that evaluates to the number of elements in an array, and countof/_Countof emerged as a clear winner: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3440.htm