Adopt SnippetString API

With the December release VS Code will have real API to define a CompletionItem that is inserted as snippet, for details see https://github.com/Microsoft/vscode/issues/3210.

In short, we now support a subset of the more common TextMate syntax: $1, $2 etc define tabstops, ${1:value} and ${2:this is${3:nested}} placeholders, and $0 is for the final tabstop.

The API for this is contained in a new type SnippetString. It can be used as the insertText of a CompletionItem.

During a transition phase we will still support the internal, unspecified snippet syntax your extension is using but eventually remove it (roughly 2 or 3 milestones from now).

The language server protocol supports the SnippetString in its next-branch - see https://github.com/Microsoft/vscode/issues/15577#issuecomment-262160802

[EisenbergEffect]

@jrieken Thanks for the heads up. We really appreciate you reaching out to us! Also, whenever you are at Microsoft’s Redmond campus in the future, ping me. I’d love to meet and talk with you about your work on VS Code.

[eriklieben]

@dbaeumer created a new branch and installation works now 😃 Thanks!

@jrieken new version of aurelia extension is on it’s way with SnippetString, sorry for the long delay.

Thanks all!