std.xml2 candidate

[Lutger Blijdestijn]

so wrote:

>> If you take into account that tango's xml parser does less validation and
>> that it is up to par with the fastest C++ parsers out there, I suggest
>> lowering the bar a little bit at first. For example, outperforming
>> libxml2.
> 
> There is no reason a D code should perform worse than C++ if you are not
> using some high level constructs.
> When it comes to strings/slicing/template, you might actually get
> performance boost comparing to C++.
> The C++ parser mentioned here (RapidXML) depends heavily on these.
> 

I know, and tango's parser is proof of that. But it can take a lot of work 
getting to that level. Right now we have an xml library a lot of people 
don't want to use, has bugs and performs 60 times worse than tango's.

Imho it's better to include it if performance is merely acceptable and see 
if it is possible to improve from there on.