Allow templates to access templateOpts via a string

[earobinson]

We could use a format like:

{
  tag: '#.tags[_id].name'
}

this would be the same as:

{
  tag: ({ object, templateOpts }) => templateOpts.tags[object._id].name
}

[earobinson]

other formats we could use are

{
  tag: '#tags[_id].name'
}

or even

{
  tag: 'templateOpts.tags[_id].name'
}

[Abhijith1995]

I personally prefer the first option since # can be a direct sub for templateOpts which makes it a bit easier to reason about in my head. But the second option's more consistent.

[iain8]

hmm i think i agree, i like the #. whereas templateOpts seems like more of an arbitrary string to remember