Add get() method to TempleContext

[maaaks]

Why don't you add a function like this into TempleContext? (This snippet does not work because of some Temple's template magic which I couldn't understand)

T get(T)(in string name, lazy T defValue=T.init)
{
    return (name in vars) ? vars[name].get!T : defValue;
}

It is for convenient usage like:

auto someBool = var.get!bool("someBool", false);  // parameter is false if not set
auto someInt  = var.get!int("someInt", -1);       // parameter is -1 if not set