added sumOfLogs

Computes accurate sum of binary logarithms of input range.
@JakobOvrum A have added `isFloatingPoint!(ElementType!Range)`.  It looks like all std.numeric without checks like `isFloatingPoint`. For example 
```D
ElementType!Range entropy(Range)(Range r) if (isInputRange!Range)
{
    Unqual!(typeof(return)) result = 0.0;
    foreach (e; r)
    {
        if (!e) continue;
        result -= e * log2(e);
    }
    return result;
}
```