Create file-system implementation for Amazon S3 storage

Allow versions of the same patch to work together

Sleet versions with the same major and minor version will work together. These will no longer require recreating and upgrading the feed.

Patch versions from now on will only contain bug fixes. New features or any breaking changes will require the minor or major version numbers to be increased.

Updating release notes to 2.2.0

Adding 2.1.0 release notes

Updating to version 2.1.0

Adding IconUrl to nuspec files

Version 2.0.0

Adding appveyor artifacts link to readme.md