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

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

The math mode for the following passage is not active:

https://geomstats.github.io/01_data_on_manifolds.html

The non-linear spaces we consider are called manifolds. A manifold :math:M of dimension :math:m is a space that is allowed to be curved but that looks like an m-dimensional vector space in the neighborhood of every point.