Add module manifest

Unfortunately I can't set the version to Beta as it is not recognized as
a valid Version.
Make module manifest compatible with PowerShell 2.0
Make module compatible with PowerShell 5.0 (and PowerShellGet and PoshCode + Chocolatey)
Add complete description from nupkg
PowerShellGet generates a nupkg from the manifest, so these need to match what you want in there.