Add Tree.find_token() method

[makukha]

Resolves #1466.

[makukha]

I put this method outside of "standalone" scope as it uses scan_values() that is not included as well. Not sure if this is correct.

[makukha]

@erezsh ready for review.

[erezsh]

Overall looks good. A few requests:

• Add a test
• Rename typ to token_type
• Clarify in the docstring that it is a recursive function, i.e. it will find tokens in all the subtrees.

[makukha]

I changed isinstance(v, Token) to not isinstance(v, Tree) (same as in _pretty()) to avoid importing Token.

@erezsh ready for review.

[erezsh]

Sorry it tooks me this long to reply! It slipped my memory.

I think it's better to keep it as isinstance(.., Token).

[erezsh]

The logic in pretty is a little different.

P.S. if you don't have time right now, let me know, and I'll make the change for you.

[makukha]

Thank you so much, @erezsh! This change is pretty simple, added it to PR.

[MegaIng]

Looks good, however I would also like to see a test for what happens if there is a leaf node that isn't a Token instance. (i.e. it doesn't get listed).

[makukha]

@MegaIng Thank you for the hint. I added a non-token item at the end of the tree. As expected, it didn't affect the result.

[erezsh]

Thanks!