Release extension under CashScript organisation

[rkalis]

We're moving CashScript/cashscript#243 into this repo:

• Create a 'CashScript' publisher on the VS Code marketplace
• Ask Nathaniel to transfer ownership of the GitHub repository
• Review Pat's code changes and merge that into the GitHub repo + review the rest of the code
• Publish extension from the new publisher
• Ask Nathaniel to deprecate the old extension in favour of the new one

[rkalis]

Nathaniel transferred the ownership of the GitHub repository last week.

Today we merged Pat's code changes into a separate branch. After that we moved the compiler stuff from antlr4ts to antlr and we copied over the latest CashScript grammar files. We also moved to yarn and added Prettier to have consistent code formatting.

Next session we want to go over the rest of the code and see if we can make improvements here and there, but regardless we want to publish the extension next session. When that is done, we'll ask Nathaniel to deprecate the old extension in favour of the new one.