Better exercises for lambda and stl

After having a longer discussion yesterday with bernhard, i got the following idea how the difficulty of understanding lambdas and stl could be eased.

I would suggest the following exercises (in order of execution):

1. lambda simple: exercise to write simple lambda function, maybe even start with rewritting an existing function by a lambda - no usage of stl
2. lambda and stl - simple: rewrite an (existing & fully functioning) program that uses stl with function object to replace these function objects with lambdas
3. lambda and stl - advanced: have an unfinished program where stl functions and their respective lambdas must be added. could be that in the readme there is a list of possible stl functions to decide from

Review the existing C++ course exercise structure before planning the three proposed lambda and STL exercises. Done means providing simple lambda, lambda-and-STL simple, and lambda-and-STL advanced exercises in the stated order, with the advanced exercise including guidance on possible STL functions.