Modifications done while reading again the formation

• Most changes are fairly minor, including /close #32 (closed)
• In Functions notebook, a more detailed explanation about declaration and definition has been added.
• Update some data to reflect 2022 standpoint
• Add Coliru links when stuff that worked in 2021 is broken in Xeus-Cling circa 2022

I hope I haven't broken anything - I made the first version of a branch following !35 (closed) and had to backport my modifications in the more senseful hierarchy used in main branch (I will take a Linux laptop for my rereading / modifications of the hands ons).

@vrouvrea @steff As usual any reviewer would do

added C++ Documentation labels

requested review from @steff

assigned to @sgilles

resolved all threads

I closed the threads after agreement with @steff that I do it myself, as I heeded the corrections suggestions except in two cases I discussed with him.

added 5 commits

• 3091dbcc - English suggestion by Laurent.
• 24ca1df6 - Modify a sentence following a suggestion by Laurent.
• cdf68e80 - Revert misguided correction.
• 2caa9a26 - Add missing punctuation.
• 9341382a - Typo corrected.

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approved this merge request

resolved all threads

merged

mentioned in commit f17fc6ce