Fix errata

[ivanpanch]

I have corrected some minor mistakes, such as a functions (instead of a function) and This a (instead of This is a).

[cubbimew]

LGTM, but CI complained here

Warning: Undesired chars (–’‘“”¸…¦) or Unicode EN SPACE found, use markdown-compatible symbols instead:
 21041	* All the talks from [CppCon ’14](https://isocpp.org/blog/2014/11/cppcon-videos-c9)

and also here (need to add the word to ./scripts/hunspell/isocpp.dic )

Warning: Spellcheck failed, fix words or add to dictionary:
Line 1432: underqualified -> under qualified

[ivanpanch]

I changed to a numeric character reference, maybe that is accepted? (The ASCII apostrophe gets replaced by an opening quotation mark at this position, so it is not suitable.)