Addition of function for C-shaped polynomial RH and perturbation on RH profiles

[stella-bourdin]

Addition of functions useful for my thesis/paper :

• A C-shaped RH profile defined with simple linear and quadratic functions
• A function to add a square or gaussian perturbation on another profile.

[lkluft]

Thanks for the review, @SallyDa 👍

We will rebase the branch before merging it to upstream/master. While doing so, we can also add Stella's Github mail :)