This Pull Request is for HacktoberFest 2020

Description of Change

Checklist

• Added description

Add quickselect algorithm. Quickselect is a selection algorithm to find the kth smallest element in an unordered list.

Welcome to JavaScript community

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that p

Description of Change

References

Checklist

Currently we've implemented a bunch of functions and constraints in a "lazy evaluation" fashion, i.e., whenever we need something for a Style program, we implement it in Penrose. We're getting to the point where we should really have a more complete/comprehensive list (e.g., that users can call at will).

How do we come up with this list? One natural idea is to simply pick some libraries, and

Explain what you would like to see improved

TCling::CheckClassInfo() should return (by parameter) the found decl, such that TClass::Init() can use it to construct the TClingClassInfo and that doesn't need to repeat the lookup.

To Reproduce

One:

#0  cling::LookupHelper::findScope (this=0x5555555f7be0, className=..., diagOnOff=cling::LookupHelper::NoDiagnostics, 
    resu

This is a list of public non-deprecated functions that are never used either directly or indirectly in the main codebase or the tests/examples.

Tests should be written for some of these functions.

If you are looking to contribute to igraph, fixing some of these is an easy way to get started. If you are unsure which one to take, just ask. [Here's a guide on writing tests.](https://github.com/