[ruby/irb] Update help message for next context-mode of 4

While here, fixing tab/space issues in help message, and sync
rdoc for IRB class to match the help message.

https://github.com/ruby/irb/commit/ef8e3901cc

lib/irb.rb

@@ -60,7 +60,11 @@ require_relative "irb/easter-egg"
 #     -E enc            Same as `ruby -E`
 #     -w                Same as `ruby -w`
 #     -W[level=2]       Same as `ruby -W`
-#     --inspect         Use `inspect' for output (default except for bc mode)
+#     --context-mode n  Set n[0-4] to method to create Binding Object,
+#                       when new workspace was created
+#     --echo            Show result(default)
+#     --noecho          Don't show result
+#     --inspect         Use `inspect' for output
 #     --noinspect       Don't use inspect for output
 #     --multiline       Use multiline editor module
 #     --nomultiline     Don't use multiline editor module
@@ -68,19 +72,24 @@ require_relative "irb/easter-egg"
 #     --nosingleline    Don't use singleline editor module
 #     --colorize        Use colorization
 #     --nocolorize      Don't use colorization
-#     --prompt prompt-mode
-#     --prompt-mode prompt-mode
+#     --prompt prompt-mode/--prompt-mode prompt-mode
 #                       Switch prompt mode. Pre-defined prompt modes are
 #                       `default', `simple', `xmp' and `inf-ruby'
 #     --inf-ruby-mode   Use prompt appropriate for inf-ruby-mode on emacs.
 #                       Suppresses --multiline and --singleline.
-#     --simple-prompt   Simple prompt mode
+#     --sample-book-mode/--simple-prompt
+#                       Simple prompt mode
 #     --noprompt        No prompt mode
+#     --single-irb      Share self with sub-irb.
 #     --tracer          Display trace for each execution of commands.
 #     --back-trace-limit n
 #                       Display backtrace top n and tail n. The default
 #                       value is 16.
+#     --verbose         Show details
+#     --noverbose       Don't show details
 #     -v, --version	    Print the version of irb
+#     -h, --help        Print help
+#     --                Separate options of irb from the list of command-line args
 #
 # == Configuration
 #

lib/irb/lc/help-message

@@ -18,7 +18,7 @@ Usage:  irb.rb [options] [programfile] [arguments]
   -E enc            Same as `ruby -E`
   -w                Same as `ruby -w`
   -W[level=2]       Same as `ruby -W`
-  --context-mode n  Set n[0-3] to method to create Binding Object,
+  --context-mode n  Set n[0-4] to method to create Binding Object,
                     when new workspace was created
   --echo            Show result(default)
   --noecho          Don't show result