Parameter names are not properly encoded for signature #19

Hi

The OAuth spec requires parameter names to be encoded using the %XX format and then URL encoded, but the code is not doing so (snippet from UriUtility.NormalizeRequestParameters):

IEnumerable orderedParameters = parameters
.OrderBy(x => x.Key, StringComparer.Ordinal)
.ThenBy(x => x.Value)
.Select(
x => new QueryParameter(x.Key, UrlEncode(x.Value)));

If a parameter name is "foo[bar]" the final encoding for the signature string should be "foo%255Bbar%255D" but the library currently produces "foo%5Bbar%5D".