/// <summary>
/// URL encode a String.
/// </summary>
/// <param name="url">The string to URL encode.</param>
/// <param name="length">Input string length;
/// use 0 for cURL to determine.</param>
/// <returns>A new URL encoded string.</returns>
/// <exception cref="System.InvalidOperationException">
/// Thrown if cURL isn't properly initialized.</exception>
public static string Escape(string url, int length)
{
EnsureCurl();
IntPtr p = External.curl_escape(url, length);
String s = Marshal.PtrToStringAnsi(p);
External.curl_free(p);
return(s);
}