[WIP] Add a folder "programs" for executables solving a single problem

[ClementPernet]

Currently the "examples" folder plays two roles:

1. demonstrate simple examples of usage of the code
2. provide binaries for solving a single problem, such as Det, Rank etc

This PR aims at separating these 2 functions, by introducing a "programs" folder in which the executables solving single problems will be located, leaving the "examples" folder to the role of simple code examples for tutorials.