feat: implement tr

[revosw]

This pull request implements the tr command, which is documented in section 9.1 tr: Translate, squeeze, and/or delete characters.

One aspect of this implementation of tr that differs from GNU coreutils is how each character is handled. GNU coreutils processes byte-for-byte, not taking into account multibyte codepoints. This implementation, however, processes codepoint-for-codepoint. Here are some examples.

echo old | tr old new: Translating a single-byte codepoint to another single-byte codepoint works the same between this implementation and GNU coreutils' implementation.

	Input	Output (V coreutils)	Output (GNU coreutils)
Codepoints	old	new	new
Bytes	111 108 100	110 101 119	110 101 119

echo ! | tr ! ❗: Translating a single-byte codepoint into a multibyte codepoint. The GNU implementation only replaces the first byte (226), which means programs that expect UTF-8 encoded data might render the replacement codepoint � (U+FFFD) in its place to represent incomplete data

	Input	Output (V coreutils)	Output (GNU coreutils)
Codepoints	!	❗	�
Bytes	33	226 157 151	226

If replacing entire codepoints is undesirable, it's very easy to revert to the byte-for-byte behavior.

As of now, this is what is implemented

• tr <arg1> <arg2>
• tr -d <arg>, tr --delete <arg>
• tr -t <arg1> <arg2>, tr --truncate-set1 <arg1> <arg2>
• tr -s <arg1> <arg2>, tr --squeeze-repeats <arg1> <arg2>
• tr -c <arg1> <arg2>, tr --complement <arg1> <arg2>

[spytheman]

The project goal is to re-implement the GNU coreutils tools behaviors as closely as possible, including error messages etc.

[JalonSolov]

However, a new option could be added, to allow proper handling of multi-byte chars.

Nothing says we can't have options they don't, just that the default, and any options they do have, should act as close to theirs as possible.