strconv: Documentation to strconv.Itoa is misleading

[jellonek]

Docstring added in efbeaed#diff-ad34fc4c548aecacd88a4f12a256a414R42 suggests that Itoa is an alias to FormatInt with decimal base, but this shorthand also transforms argument from int type into int64 (what shortens input data value range in default implementation).

This comment IMO should be extended to clearly inform that input data format is changed (that is visible in functions signatures as in source of this function, but what can be easily overlooked).