add support for emoji compilation in formatted arguments

[bobheadxi]

I have some structs that implement String() string, where String() could return something that contains an emoji. However, when doing something like:

// type C implements String() string
Printf(":rocket: am I %s?\n", C("coloured :rocket:", RD, UL))
//  🚀  am I coloured :rocket:?

this happens because arguments to Printf or anything that takes ...interface{} are compiled separately argument-by-argument (example), and only compiles emojis if it is a string:

func compileValues(a *[]interface{}) {
	for i, x := range *a {
		if str, ok := x.(string); ok {
			(*a)[i] = compile(str)
		}
	}
}

there are 2 ways to support this:

• in compileValues, check for String() via type assertion and compile that
• call Sprint or the required variation of it before compiling, and make compile the last step before a print in every case

this PR implements the 2nd method, which I think is the cleanest and most consistent way to do it - if you prefer the other way, or have other ideas, I would be happy to implement it.

thanks!

[kyokomi]

@bobheadxi Thank you for fixing. I think that this content is good. 👍