Merge branch 'readCString' into 'master'

A small string overhaul

This commit adds functions to:
- Append strings of fixed size
- Read strings with or without a trailing `\0`

There is also a string-related fix for the function management service.

This takes care of issues #43 and #11.

Don't mind the irrelevant commits, they show up because `ci-1` is not merged to master yet.

See merge request acubesat/obc/ecss-services!41