reorg Silver sorting and searching modules, move some modules to Gold

[bqi343]

TODO: read through Silver and Gold sorting / ds sections again to check that ordering of topics makes sense.

Place an "x" in the corresponding checkbox if it is done or does not apply to this pull request.

• I have tested my code.
• I have added my solution according to the steps here.
• I have followed the code conventions mentioned here.
  • I understand that if it is clear that I have not attempted to follow these conventions, my PR will be closed.
  • If changes are requested, I will re-request a review after addressing them.
• I have linked this PR to any issues that it closes.

[SansPapyrus683]

most of the problems in the pq module use sets

[bqi343]

I am rewriting some of the internal sols to remove the sets (William and Robots, Convention II). There is no reason to use sets here.

I don't think any other internal sols use sets.

[SansPapyrus683]

can i ask for proof of ac?

[bqi343]

I have resubmitted all the code I modified.

[bqi343]

most of the problems in the pq module use sets

@SansPapyrus683 does it look good now?

[SansPapyrus683]

should difficulty be updated

[bqi343]

difficulty of what?

[bqi343]

feel free to change them if you want (or not)

[SansPapyrus683]

eh, i suppose i'll get used to this with time