Why are so many `class XMLUtil` members inline?

[Dmitry-Me]

I see that even StringEqual() is declared inline. Is that necessary? What would happen if it was inside the .cpp?

[leethomason]

There was some intent for performance, but it went too far. And clutters the headers. I'd support moving the larger ones (StringEqual) inline, but leave the small ones (IsUTF8Continuation.)