Support -n (--no-newline) option

[ko1nksm]

I found out here that the minimal implementation of readlink has the -f and -n options.

https://man.openbsd.org/readlink.1

The readlink utility when invoked with the pathname of a symbolic link as its argument dereferences the symbolic link and prints the name of target on standard output. If the -f option is not specified and readlink is invoked with an argument other than the pathname of a symbolic link, it exits with a nonzero exit code without printing anything.

The options are as follows:

-f
Canonicalize by following every symlink in every component of the given path recursively. readlink will resolve both absolute and relative paths and return the absolute pathname corresponding to file. The argument does not need to be a symbolic link.
-n
Do not print a trailing newline character.

I will support the -n option because it is needed when handling correctly with filenames ending in newline. To be precise, I will create readlinkfn function instead of adding a option.