convert CamelCase to camel_case.

CombineSortedWithSep combines a slice of strings into a single string, with the given separator between each string.

CompareStringPointer compare string pointer return true if a and b are both nil or a == b.

格式化golang代码，包括import.

GetStringByPointer get string by pointer return "" if pointer is nil.

encode json.

convert first letter to lower case.

Reference: https://xie.infoq.cn/article/f274571178f1bbe6ff8d974f3.

convert first letter to upper case.