Add Trinomial Triangle hole

[MeWhenI]

Description

Print the first 20 rows of the Trinomial Triangle.

Rationale

I think this presents a challenge that is different enough from Pascal's and Lucky Tickets to have unique & interesting solutions in many langs. In particular, I believe a lot of langs have tricks for Pascal's that fail to generalize.

As far as I can see, there are not easily found spoilers for this challenge on anagol or CGSE.

Also, the recent holes tab is in my opinion saturated with holes that are generally much more complex than average for code.golf. I think a simpler hole would be nice.

[kg583]

It could use a lengthier description, given that most probably haven't heard of the trinomial triangle. Even a cursory description like for Pascal's Triangle would be worthwhile.