Document the API as “C++”, not “C”

[edgar-bonet]

The Red Pitaya C API has been replaced by a C++ API. The February 2026 update to the documentation does mention this fact. However, there are still lots of pages that incorrectly mention a “C API”.

This pull request replaces “C” by “C++” in many places where this is relevant. Note however that:

• it does not touch the many mentions of “C” within appsFeatures/examples, as I did not test these examples with a C++ compiler

• it does not rename the files C_and_Python_API.{rst,inc}

Fixes: #87.

For the record, mentions of “C” can be found with the command below, but beware of the many false positives:

find . -name '*.rst' -o -name '*.inc' | sort | \
    xargs grep --color=always '\<C[^0-9A-Za-z_`:+]' | less -R

[Lightsaver7]

Oh, I see what you mean. Yes, I missed those during the update. I will merge this and check if there are any other places where this applies.