(https://github.com/ruby/irb/pull/877)
* Make help command display help for individual commands
Usage: `help [command]`
If the command is not specified, it will display a list of all available commands.
If the command is specified, it will display the banner OR description of the command.
If the command is not found, it will display a message saying that the command is not found.
* Rename test/irb/cmd to test/irb/command
* Add banner to edit and ls commands
* Promote help command in the help message
1. Make `show_cmds` an alias of `help` so it's not displayed in the help message
2. Update description of the help command to reflect `help <command>` syntax
* Rename banner to help_message
43a2c99f3f
(https://github.com/ruby/irb/pull/873)
* Replace ExtendCommand with Command and standardize command related names
1. Rename lib/irb/extend-command.rb to lib/irb/command.rb
2. Rename lib/irb/cmd/*.rb to lib/irb/command/*.rb
3. Rename test/irb/test_cmd.rb to test/irb/test_command.rb
4. Rename ExtendCommand to Command
* Alias ExtendCommand to Command and deprecate it
* Rename Command::Nop to Command::Base
* Not deprecate old constants just yet
* Add lib/irb/cmd/nop.rb back
462c1284af
