(https://github.com/ruby/irb/pull/783)

With either `IRB.conf[:USE_PAGER] = false` or `--no-pager` commnad line flag.

I decided use `--no-pager` instead of `--use-pager` because it matches with
Pry and git's command line flags.

https://github.com/ruby/irb/commit/df1c3b9042

(https://github.com/ruby/irb/pull/754)

* Add command line option to select which completor to use

* Add test for completor argv

https://github.com/ruby/irb/commit/1dec2708c9

https://github.com/ruby/irb/commit/a55ace0791

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

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

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

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