Specify the MaxIdleTime to prevent a WebException

Per the Litle XML Reference Guide section 2.3.2.4 the Litle servers will
close persistent connections after 10 seconds. Set the MaxIdleTime
property on the web request service point to prevent GetResponse() from
throwing [WebException: The underlying connection was closed: A
connection that was expected to be kept alive was closed by the server.]
after the connection is forcibly closed by the server.
Disable Expect100Continue for Litle only

Disable the Expect100Continue property on the Litle service point. The
ServicePointManager.Expect100Continue property affects all web requests
in the application. Some applications rely on the Expect: 100-continue
header to operate properly (e.g. ASP.NET Web Services clients).
Merge pull request #19 from lmikkelsen/master

Improved HttpPost() method