Add PSBuild to the PowerShell Gallery

[hmmwhatsthisdo]

The PowerShell Gallery is a package-distribution system designed specifically for PowerShell modules and scripts. While NuGet provides one option for distributing .NET/C++ packages, PSGallery is more tightly integrated with PowerShell 5.0 and above.

Getting PSBuild on the PowerShell Gallery would mean anyone running PowerShell 5.0 or above could install the module simply by running Install-Module PSBuild - no initialization scripts or the like required.