Provide separate targets for publishing to MyGet, NuGet and Chocolatey

[CharliePoole]

When failures occur in the release process, it's sometimes necessary to re-run individual steps. Currently, the Publish target tries to publish to all the sites we use and re-running causes errors if some steps were successful and others failed.

[CharliePoole]

This issue has been resolved in version 4.0.0-beta.2

The release is available on:
GitHub.
NuGet packages are also available NuGet.org and
Chocolatey Packages may be found at Chocolatey.org