push/pull: rename `channel` option

Dependencies

• [2] AEPEFS7O Write help for each argument
• [3] 5HF7C67M push/pull: fixed "changes" arguments
• [4] KWAMD2KR A few fixes in the documentation comments
• [5] 76PCXGML Pushing to, and pulling from the local repository
• [6] I52XSRUH Massive cleanup, and simplification
• [7] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).
• [8] VMPAOJS2 Don't output after pushing to a local channel
• [9] 4H2XTVJ2 Fix some mistakes in the docs

Change contents

• replacement in pijul/src/commands/pushpull.rs at line 61
  [2.1677]→[3.113142:113201](∅→∅),[3.113142]→[3.113142:113201](∅→∅)
  − #[clap(long = "channel")]

  − channel: Option<String>,
  [2.1677]

  [2.1678]
  + #[clap(long = "from-channel")]

  + from_channel: Option<String>,
• replacement in pijul/src/commands/pushpull.rs at line 88
  [2.2166]→[3.113632:113691](∅→∅),[3.113632]→[3.113632:113691](∅→∅)
  − #[clap(long = "channel")]

  − channel: Option<String>,
  [2.2166]

  [2.2167]
  + #[clap(long = "to-channel")]

  + to_channel: Option<String>,
• replacement in pijul/src/commands/pushpull.rs at line 121
  [3.114607]→[3.114607:114690](∅→∅)
  − let channel_name = repo.config.get_current_channel(self.channel.as_ref());
  [3.114607]

  [3.114690]
  + let channel_name = repo.config.get_current_channel(self.from_channel.as_ref());
• replacement in pijul/src/commands/pushpull.rs at line 268
  [3.117701]→[3.117701:117784](∅→∅)
  − let channel_name = repo.config.get_current_channel(self.channel.as_ref());
  [3.117701]

  [3.117784]
  + let channel_name = repo.config.get_current_channel(self.to_channel.as_ref());