Since it has a functional role, we can not just replace it, we must keep
it around. This also allows us to simplify the code slightly.
We must fix this before we fix#1438 since otherwise the \n will be
missing with --style=plain, since we will stop adding it if it is
missing.
Adds a new `-A`/`--show-all` option (in analogy to GNU Linux `cat`s option) that
highlights non-printable characters like space, tab or newline.
This works in two steps:
- **Preprocessing**: replace space by `•`, replace tab by `├──┤`, replace
newline by ``, etc.
- **Highlighting**: Use a newly written Sublime syntax to highlight
these special symbols.
Note: This feature is not technically a drop-in replacement for GNU `cat`s
`--show-all` but it has the same purpose.
