Add examples of Hack APIs

[ChrisYanY]

can we put some code example for each of the hack api? Too few public usage out there. Solely looking at the api without examples could be real pain.

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Please don't change anything below this point.

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• Build ID: 2019-03-15T20:34:09+0000:361688e6c740dea5615800d530efcf4090ad0b4c
• Page requested: /hsl/reference/function/HH.Lib.Str.split/
• Page requested at: Wed, 27 Mar 2019 18:22:15 +0000
• Controller: APIClassPageController

[kunalb6]

I don't see any of the HSL APIs have an examples section, can someone give me a few code pointers to get started with implementing these?