Generate terminals by shuffling fomulas

[soulne4ny]

Background

Currently we drop terminals randomly. And even if we find good weights [#13], it might still be hard to play.

Proposal

• Create a queue of next terminals.
• When the queue lacks terminals,
  • choose 3 final compound formulas from the registry,
  • randomly shuffle their terminals
  • and add to the queue.
• Show next 3 elements.

This will guarantee that the stuff on the board has a good chance to produce compounds.

Derived from #13 & #18.

[soulne4ny]

$ git push -f origin i24
Counting objects: 23, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (9/9), done.
Writing objects: 100% (12/12), 2.34 KiB, done.
Total 12 (delta 2), reused 9 (delta 0)
To git@github.com:yarcat/chemistry-lines.git
 + 10bd751...d41bece i24 -> i24 (forced update)

[soulne4ny]

This feels nicer that random, specially with --min-elements. However it looks like we should try to remove compounds manually.

[soulne4ny]

Yar, please, review it.

[yarcat]

Generally looks good, please address two comments that I've left there. The second one is definitely optional, and can be implemented later (or even never implemented).