Portability part 1 - C99 printf

printf, sprintf, fprintf etc are now all C99 compliant. All except sprintf, which is now signaled as deprecated. This raises a few warnings about sprintf usage in the build. Some I fix with pull requests that will follow. Some others should be fixed by the respective authors.
(Pre-existing) I would be happier with the formatting if later lines were indented to sit under the first word of the `*`-line, i.e.
```
* Pull ...
  pull-requests ...
  longer.
```
... but perhaps mark-down isn't cool with that ?