Be less hand-hold-y with New-Release because there are some limitations:

The EnvDTE operations for building a project do not block on Windows 7 (Powershell v2), so our attempts to clean up stale packages and build them are flawed for some users.

Let's opt-in if you're running Powershell v3 or later. Fixes an issue raised in #177 but does not resolve it.

Oh, and I'm cleaning the solution too. Resolves #167. 

Ping @peters