Adding Threaded Binary Tree and Priority Queue implementations

[Korra15]

Greetings ma’am/sir,
Going through the list of algorithms, I could not find any implementation of threaded binary tree or priority queues. Could I start working on these algorithms?

[ak14bbk30]

yes sure

[onlinejudge95]

Make sure to split the implementation into separate PRs

[Korra15]

okay