commands: set up pager for diff, change, and credit

Dependencies

• [2] L4JXJHWX pijul/*: reorganize imports and remove extern crate
• [3] 23LVKATN Use pager crate for log output
• [4] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• replacement in pijul/src/commands/log.rs at line 40
  [4.135434]→[3.19:66](∅→∅)
  − Pager::with_pager("less -rF").setup();
  [4.135434]

  [4.135434]
  + Pager::with_pager("less -F").setup();
• edit in pijul/src/commands/diff.rs at line 8
  [2.2654]

  [2.2654]
  + use pager::Pager;
• edit in pijul/src/commands/diff.rs at line 83
  [4.175777]

  [4.175777]
  + Pager::with_pager("less -F").setup();
• edit in pijul/src/commands/credit.rs at line 8
  [2.2844]

  [4.178929]
  + use pager::Pager;
• edit in pijul/src/commands/credit.rs at line 52
  [4.180284]

  [4.180284]
  + Pager::with_pager("less -F").setup();
• edit in pijul/src/commands/change.rs at line 7
  [4.189446]

  [2.3124]
  + use pager::Pager;
• edit in pijul/src/commands/change.rs at line 37
  [4.190976]

  [4.190976]
  + Pager::with_pager("less -F").setup();