Missing dependencies for package `forest`

[G. Cassian Alexandru]

Hi,

it seems that `forest` is has undeclared dependencies. Judging from
https://github.com/sasozivanovic/forest/blob/master/forest.dtx, they
seem to be:

pgfopts, etoolbox, environ, xparse, and inlinedef.

Cheers, Cassian

PS: Just checking, this _is_ the right way to go about this, no? I would
also happily submit a pull request or similar when I encounter issues
like this in the future. (I am a bit obsessed with project specific,
minimal tex installations (using `nix`), so I encounter these kind of
issues quite frequently).