Support dollar sign or at sign ?

[gauss02]

json data;
data["name"] = "name";
data["name"] = "name";
data["$name"] = "$name";
data["@name"] = "@name";
data["$name"] = "$name";
data["@name"] = "@name";
std::cout<<data.dump(2) <<std::endl;
std::cout<<render("Hello 1 {{ name }}!", data) <<std::endl;
std::cout<<render("Hello 2 {{ _name }}!", data) <<std::endl;
std::cout<<render("Hello 3 {{ $name }}!", data) <<std::endl;
std::cout<<render("Hello 4 {{ @name }}!", data) <<std::endl;
std::cout<<render("Hello 5 {{ _$name }}!", data) <<std::endl;
std::cout<<render("Hello 6 {{ _@name }}!", data) <<std::endl;

{
"$name": "$name",
"@name": "@name",
"$name": "$name",
"@name": "@name",
"_name": "_name",
"name": "name"
}
Hello 1 name!
Hello 2 _name!
Hello 3 name!
Hello 4 name!
terminate called after throwing an instance of 'inja::RenderError'
what(): [inja.exception.render_error] (at 1:12) malformed expression

[pantor]

This should be fixed with the latest commit. Thanks for the feedback!