base64: Implement -w/--wrap

This is an option supported by coreutils, so we might as well support
it too.

It allows users to wrap their encoded output after the "column" value
they provide.

This commit also has the Markdown look more like what we see
when running ArgsParser::print_usage_markdown() (and it fixes some
of the examples).

Userland/Utilities/base64.cpp

@@ -10,15 +10,29 @@
 #include <LibCore/System.h>
 #include <LibMain/Main.h>
 
+static void print_wrapped_output(size_t column, StringView encoded)
+{
+    VERIFY(column > 0);
+
+    while (!encoded.is_empty()) {
+        auto segment_length = min(column, encoded.length());
+
+        outln("{}", encoded.substring_view(0, segment_length));
+        encoded = encoded.substring_view(segment_length);
+    }
+}
+
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     TRY(Core::System::pledge("stdio rpath"));
 
     bool decode = false;
+    Optional<size_t> maybe_column;
     StringView filepath = {};
 
     Core::ArgsParser args_parser;
     args_parser.add_option(decode, "Decode data", "decode", 'd');
+    args_parser.add_option(maybe_column, "When encoding, wrap output after column characters", "wrap", 'w', "column");
     args_parser.add_positional_argument(filepath, "", "file", Core::ArgsParser::Required::No);
     args_parser.parse(arguments);
 
@@ -34,6 +48,12 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     }
 
     auto encoded = TRY(encode_base64(buffer));
+
+    if (maybe_column.has_value() && *maybe_column > 0) {
+        print_wrapped_output(*maybe_column, encoded);
+        return 0;
+    }
+
     outln("{}", encoded);
     return 0;
 }