Autoload

[tubaterry]

We can now read in an existing TOC when loading a markdown file.

• New addition: Activate when markdown grammar gets used

• On Activation, check all existing textEditors for markdown and assign a Toc object per textEditor using markdown. (Previously the Toc object was assigned to paneItems).

• On addition of new text editors (onDidAddTextEditor callback), check if it's using markdown and assign Toc object if necessary.

Downside: this could be more efficient - first textEditor to load a markdown file runs through init twice (on both activate hook and onDidAddTextEditor callback)

[tubaterry]

@nok - Just pinging you because this repo hasn't seen any activity in a while, wanted to make sure it didn't get lost

[tubaterry]

Not ready yet - Selecting Add adds a TOC at the cursor position of every open markdown file.