feat: diff of states

Added first subcommand - diff.
It allows to check how diffrent
current state of machine is in
compareson to world file.

src/package_manager.rs

@@ -0,0 +1,30 @@
+use crate::{error::Result, world::Packages};
+use std::process::{Command, Stdio};
+
+pub fn get_system_state() -> Result<Packages> {
+    let command = Command::new("pacman")
+        .arg("-Qqe")
+        .stdout(Stdio::piped())
+        .output()?;
+
+    let official: Vec<String> = String::from_utf8(command.stdout)?
+        .split_whitespace()
+        .map(|x| x.to_owned())
+        .collect();
+
+    let command = Command::new("pacman")
+        .arg("-Qqm")
+        .stdout(Stdio::piped())
+        .output()?;
+
+    let foreign: Vec<String> = String::from_utf8(command.stdout)?
+        .split_whitespace()
+        .map(|x| x.to_owned())
+        .collect();
+
+    Ok(Packages {
+        official,
+        foreign,
+        ignore: Vec::new(),
+    })
+}