If the input file is invalid (example: `grim` did not work due to
invalid geometry), handle the error gracefully.
Previously we had a coredump due to `g_error`.
Compute maximum width and height of area container based on monitor size
and fix image ratio based on appropriate values.
Note that this will lower the resolution of the final image.
Closes#56
This allows a user to output the final surface to `stdout` using:
- `-0`
- `--output-file``
Also adding another keybinding to exit the application `Ctrl+w` which is
pretty standard.
Closes#2