Fixed an XML external entity (XXE) vulnerability.

Fixed an issue that prevented AutoUpdater.NET from working when Assem…

…blyTitle was in Chiense and HttpUserAgent wasn't defined. This resolves ravibpatel#314, resolves ravibpatel#311 and resolves ravibpatel#310.

 Italian translations fix (ravibpatel#304)

Italian translations fix (ravibpatel#299)

Now using ZipStorer NuGet package for ZipExtractor.

Now using NoCacheNoStore policy for all web client requests.

Updated appveyor.yml.

Handled possible NotSupportedException on SecurityProtocol assignment…

…. This fixes ravibpatel#241.

Updated test project NuGet packages.

Added ShowUpdateForm() method call example in README.md.