Line highlighting

Put line numbers in braces after the language. The highlighted lines stay normal and the others are dimmed.

```ts {2,3}
const a = 1
const b = 2
const c = 3
const d = 4
```

Separate ranges with | to move through them, one range per click:

```ts {1|3-4|all}
const a = 1
const b = 2
const c = 3
const d = 4
```

• A range is a line (2), a list (2,3) or a span (3-4).
• all shows every line normally. hide shows nothing. * highlights nothing and keeps every line normal.
• Each | adds one click to the slide.
• In the options brace, at is the first click of the ranges (default +1) and finally is what is shown after the last click: last, all, hide or a range. Example: {1|2} {at:'+1', finally:'last'}.

Options go in a second brace, so {2,3|5|all} {lines:true} is valid.