Problem:
- Functions are duplicated in [PBM,PGM,PPM]Loader class
implementations. They are functionally equivalent. This does not
follow the DRY (Don't Repeat Yourself) principle.
Solution:
- Factor out the common functions into a separate file.
- Refactor common code to generic functions.
- Change `PPM_DEBUG` macro to be `PORTABLE_IMAGE_LOADER_DEBUG` to work
with all the supported types. This requires adding the image type to
the debug log messages for easier debugging.
Problem:
- `Streamer` is the same in [PBM,PGM,PPM]Loader class implementations.
Solution:
- Extract it to its own header file to reduce maintenance burden.
- Implement `read` in terms of `read_bytes` to make the class "DRY".
- Decorate all functions with `constexpr`.
Problem:
- `(void)` simply casts the expression to void. This is understood to
indicate that it is ignored, but this is really a compiler trick to
get the compiler to not generate a warning.
Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.
Note:
- Functions taking a `(void)` argument list have also been changed to
`()` because this is not needed and shows up in the same grep
command.
