tasks for single file

[keyring]

I want to make a task to build a single file, like a lua script file. But seems like, the tasks.json must under a folder's .vscode.

I don't want to open a folder and create many same tasks.json each time when I just new a temp single file.

May tasks.json become a extension option like sublime's build system?

[ghost]

Needs "tasks" tag?

[egamma]

@ghost added the label, thanks

[dbaeumer]

Dups #1435.