* doc: avoid use of GCC's old syntax (`-Wgnu-designator`)
* doc: highlight shell commands
* doc: point the C++ docs to v8.12
* doc: avoid highlight on output matching bash keywords
Just some issues I found while testing the examples:
- Reference on header for the file try255.py
- Typo on parameter from bigtif to bigtiff
- Use explicit call to python interpreter from command line
