Fixing a panic with reset --dry-run and no input

Dependencies

• [2] L4JXJHWX pijul/*: reorganize imports and remove extern crate
• [3] SNZ3OAMC use native external subcommand support instead of hand-rolled one
• [4] NLGQAH4H Credit and reset relative to current directory instead of the root
• [5] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• edit in pijul/src/main.rs at line 144
  [3.86849]→[3.86849:86917](∅→∅)
  − #[error("Cannot dry-reset multiple files")]

  − CannotDryReset,
• edit in pijul/src/commands/reset.rs at line 3
  [2.1314]

  [2.1314]
  + use anyhow::bail;
• replacement in pijul/src/commands/reset.rs at line 49
  [3.98844]→[3.98844:98940](∅→∅)
  − if self.files.len() > 1 {

  − return Err(Error::CannotDryReset.into());
  [3.98844]

  [3.98940]
  + if self.files.len() != 1 {

  + bail!("reset --dry-run needs exactly one file");