Hide `pijul lock` and avoid panics when used improperly

Dependencies

• [2] JL4WKA5P Implement the Sanakirja concurrency model in a cross-process way
• [3] W5NU4F6J Less noisy lock
• [*] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• edit in pijul/src/main.rs at line 124
  [2.4591]

  [2.4591]
  + #[clap(setting = AppSettings::Hidden)]
• edit in pijul/src/commands/lock.rs at line 3
  [2.7225]→[2.7225:7245](∅→∅)
  − use std::io::Write;
• replacement in pijul/src/commands/lock.rs at line 27
  [2.7769]→[2.7769:7826](∅→∅)
  − .open(&lock.as_ref())

  − .unwrap();
  [2.7769]

  [2.7826]
  + .open(&lock.as_ref())?;
• replacement in pijul/src/commands/lock.rs at line 31
  [2.7915]→[2.7915:7979](∅→∅)
  − let listener = UnixListener::bind(&self.path).unwrap();
  [2.7915]

  [2.7979]
  + let listener = UnixListener::bind(&self.path)?;
• replacement in pijul/src/commands/lock.rs at line 109
  [2.13197]→[2.13197:13263](∅→∅)
  − let lockfile = OpenOptions::new()
  [2.13197]

  [2.13263]
  + if let Ok(lockfile) = OpenOptions::new()
• replacement in pijul/src/commands/lock.rs at line 113
  [2.13419]→[2.13419:13466](∅→∅),[2.13466]→[2.13466:13531](∅→∅)
  − .unwrap();

  − lockfile.unlock().unwrap_or(());
  [2.13419]

  [2.13531]
  + {

  + lockfile.unlock().unwrap_or(());

  + }
• replacement in pijul/src/commands/lock.rs at line 129
  [2.13945]→[2.13945:14001](∅→∅)
  − .open(lock.as_ref())

  − .unwrap();
  [2.13945]

  [2.14001]
  + .open(lock.as_ref())?;