Utilities: Add an implementation of 'comm'

Add an implementation of 'comm' -- compare files line by line

Base/usr/share/man/man1/comm.md

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+## Name
+
+comm - compare two sorted files line by line
+
+## Synopsis
+
+```**sh
+$ comm [options...] <file1> <file2>
+```
+
+## Description
+
+`comm` compares two **sorted** files specified by `file1` and `file2` line by line alphabetically. One of file1 and file2, but not both, can be `-`, in which case `comm` will read from the standard input for that file.
+
+With no options, `comm` produces a three column output, indented by tabs, of lines unique to `file1`, lines unique to `file2`, and lines common to both files. `comm` provides options to suppress the output of a specific column, use case insensitive comparison or print a summary.
+
+## Options
+
+* `-1`: Suppress the output of column 1 (lines unique to `file1`)
+* `-2`: Suppress the output of column 2 (lines unique to `file2`)
+* `-3`: Suppress the output of column 3 (lines common to `file1` and `file2`)
+* `-i`: Use case insensitive comparison of lines
+* `-c`, `--color`: Always print colored output even if the standard output is not a tty
+* `--no-color`: Do not print colored output
+* `-t`, `--total`: Print a summary
+
+## Arguments
+
+* `file1`: First file to compare. (`-` for the standard input)
+* `file2`: Second file to compare. (`-` for the standard input)
+
+## Examples
+
+```sh
+# Files should be sorted first
+$ sort < file1 > file1_sorted
+$ sort < file2 > file2_sorted
+
+# Display the default three-column output
+$ comm file1_sorted file2_sorted
+
+# Read one sorted file from the standard input
+# and only display column 3
+$ sort < file1 | comm -12c - file2_sorted | less
+
+# Use case insensitive comparison,
+# suppress output of all columns
+# and print a summary
+$ comm -123it file1_sorted file2_sorted
+```