Support int as attributes and children

[Majsvaffla]

I think it would be nice if htpy supported int both as attribute value and as children. Since it's a builtin type it seems reasonable. You could argue that float and datetime should be supported too. The difference is however that it isn't obvious how to output/format those types. They heavily depend on locale for one thing.

The line between what types htpy should support and not has to be drawn somewhere but I think int doesn't cross that line 😄