ps: Add command ps

[Krysztal112233]

fix #102

[Krysztal112233]

This command is very complex and flexible (the manpage has 790~830 lines in total), so for now only the most basic functions are implemented :(

[cakebaker]

That's fine :)

[cakebaker]

I noticed you made some refactorings to pgrep. If they are unrelated to ps, I suggest to move those changes to its own PR so they can be merged independently of this PR.

[cakebaker]

Another bug I noticed is that the header row is empty if there are no options:

$ cargo run -q ps
                          
 2406   pts/3  00:00:01  konsole 
 2423   pts/3  00:00:00  bash 
 21330  pts/3  00:00:00  procps 
$ ps
    PID TTY          TIME CMD
   2423 pts/3    00:00:00 bash
  21333 pts/3    00:00:00 ps

[Krysztal112233]

Another bug I noticed is that the header row is empty if there are no options:

$ cargo run -q ps
                          
 2406   pts/3  00:00:01  konsole 
 2423   pts/3  00:00:00  bash 
 21330  pts/3  00:00:00  procps 
$ ps
    PID TTY          TIME CMD
   2423 pts/3    00:00:00 bash
  21333 pts/3    00:00:00 ps

Fixed

❯ cargo run ps
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s
     Running `target/debug/procps ps`
 PID     TTY    TIME      CMD 
 5392    pts/0  00:00:01  zsh 
 5415    pts/0  00:00:00  zsh 
 5462    pts/0  00:00:00  zsh 
 5463    pts/0  00:00:00  zsh 
 5465    pts/0  00:00:00  gitstatusd-linu 
 766725  pts/0  00:00:00  procps 

❯ ps
    PID TTY          TIME CMD
   5392 pts/0    00:00:10 zsh
   5415 pts/0    00:00:00 zsh
   5462 pts/0    00:00:00 zsh
   5463 pts/0    00:00:01 zsh
   5465 pts/0    00:00:07 gitstatusd-linu
 766859 pts/0    00:00:00 ps

[cakebaker]

Thanks :)