Use RFC2822 date formatting in `log`, `tag`, and `record --timestamp`

Dependencies

• [2] 3FTEGCMR add timestamp_validator to tag --timestamp option
• [3] F2S6XETO Fixing log --hash-only
• [4] E6IKUIPD Command to delete a tag
• [5] QL6K2ZM3 Tags
• [6] 4H2XTVJ2 Fix some mistakes in the docs
• [7] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).
• [8] OU6JOR3C Add path filtering for log, add json output for log
• [9] GUL4M5FI Cleanup and formatting
• [10] NS36CJCO Validating timestamps in record

Change contents

• replacement in pijul/src/commands/tag.rs at line 4
  [4.150]→[2.0:50](∅→∅)
  − use crate::commands::record::timestamp_validator;
  [4.150]

  [4.150]
  + use crate::commands::record::parse_datetime_rfc2822;
• replacement in pijul/src/commands/tag.rs at line 42
  [4.1086]→[2.51:120](∅→∅)
  − #[clap(long = "timestamp", validator = timestamp_validator)]
  [4.1086]

  [4.1122]
  + #[clap(long = "timestamp", value_parser = parse_datetime_rfc2822)]
• replacement in pijul/src/commands/record.rs at line 37
  [4.863]→[4.0:65](∅→∅)
  − #[clap(long = "timestamp", validator = timestamp_validator)]
  [4.863]

  [4.102495]
  + #[clap(long = "timestamp", value_parser = parse_datetime_rfc2822)]
• replacement in pijul/src/commands/record.rs at line 52
  [4.102760]→[2.121:194](∅→∅),[2.194]→[4.128:230](∅→∅),[4.128]→[4.128:230](∅→∅),[4.230]→[4.314:341](∅→∅),[4.341]→[4.256:266](∅→∅),[4.256]→[4.256:266](∅→∅)
  − pub(crate) fn timestamp_validator(s: &str) -> Result<(), &'static str> {

  − if let Ok(t) = s.parse() {

  − if chrono::NaiveDateTime::from_timestamp_opt(t, 0).is_some() {

  − return Ok(());

  − }
  [4.102760]

  [4.266]
  + pub(crate) fn parse_datetime_rfc2822(s: &str) -> Result<i64, &'static str> {

  + if let Ok(ts) = chrono::DateTime::parse_from_rfc2822(s) {

  + return Ok(ts.timestamp())
• replacement in pijul/src/commands/log.rs at line 236
  [3.1636]→[3.1636:1693](∅→∅)
  − writeln!(f, "Date: {}", timestamp)?;
  [3.1636]

  [3.1693]
  + writeln!(f, "Date: {}", timestamp.to_rfc2822())?;