feat: add C implementation for stats/base/ndarray/smean

[AtharvaPatange]

Resolves None.

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• feat: add C implementation for stats/base/ndarray/smean

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• #{{TODO: add related issue number}}

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[Sachinn-64]

@AtharvaPatange There seems to be missing implementation for examples/c/example.c.
Also noticed changes in README.md, package.json, lib/main.js as well as lib/native.js. Refer https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/ndarray/smax