First fully working cross-platform build

This build is purely PowerShell Core, and (I apologize for this) is based on PowerShell 6.0.1

A new point release for 6.0.2 is due, and I'll get it done later this week -- but I wanted to finally get this out.

Pre-release package for PowerShell Core Beta 4

Update to PowerShell Core Beta 4 references.

Fixed #8, #9, #10, error handling, as well as the build and release steps.

Refactor and cleanup of the Jupyter-Kernel assembly.

Add Write-Jupyter command to handle custom output.

The chocolatey package (nupkg) is only attached here for a few testers.

Error handling fixes

Fixed #3 #6 #7 and this release should address #5

Hopefully in this release I've packaged it correctly -- at least for people who already have the right versions of .NET Core and PowerShell Core installed.

First preview release

I've finally gotten this working for Windows PowerShell (full framework) and PowerShell Core, and I'm providing a package with an install script. You need to unzip to a permanent location, and then run the install.ps1 script from that location.