https://github.com/ruby/irb/commit/f09a1874b6

Also add --script option to turn the option back on.

Previously there wasn't a way to get an interactive IRB session
and access arguments provided on the command line.

Additionally, handle `-` as script as stdin. In Unix-like tools, `-`
means to take standard input instead of a file.  This doesn't
result in exactly the same output for:

```
echo 'p ARGV' > args.rb; irb args.rb a b c
```

and

```
echo 'p ARGV' | irb - a b c
```

Due to how irb handles whether stdin is a tty.

However, this change allows use of `-` as a argument, instead of
giving an unrecognized switch error. This required some small
changes to context.rb (to handle `-` as standard input) and
input-method.rb (to have FileInputMethod accept IO arguments in
addition to strings).

Implements [Feature #15371]

https://github.com/ruby/irb/commit/4192683ba2

* Include updated help message

https://github.com/ruby/irb/commit/ff129f3794

Changed:

    Added text to options that said just 'same as ruby -whatever'.
    Added defaults.
    Removed an errant tab.

https://github.com/ruby/irb/commit/dfe454cc33

If this is at the top level, it stops the documentation of the
entire module, but not only the part in this file.

https://github.com/ruby/irb/commit/86c41b06ad

https://github.com/ruby/irb/commit/5018f2cb99

https://github.com/ruby/irb/commit/5af637b3c1

https://github.com/ruby/irb/commit/973bac83ff

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