Add CLI and Fibonacci scripts, and implement Rectangle area calculation (#129)

Introduce a command-line interface for message printing, a Fibonacci
sequence generator, and a Rectangle class with area calculation
functionality.

## Summary by Sourcery

Introduce three standalone Ruby scripts: a CLI utility for message
printing, a Fibonacci sequence generator, and a Rectangle class under an
Area module for computing area.

New Features:
- Add a command-line interface script for printing a customizable
message multiple times
- Implement a Fibonacci sequence generator script that prompts for input
and outputs the sequence
- Introduce an Area module and Rectangle class with an area calculation
method and demonstration

Author: x0lg0n

Ruby/cli.rb

@@ -0,0 +1,18 @@
+# cli.rb
+require 'optparse'
+
+options = { times: 1 }
+OptionParser.new do |opts|
+  opts.banner = "Usage: cli.rb [options]"
+
+  opts.on("-nN", "--number=N", Integer, "Number of times") do |n|
+    options[:times] = n
+  end
+
+  opts.on("-mMSG", "--message=MSG", "Message to print") do |m|
+    options[:message] = m
+  end
+end.parse!
+
+msg = options[:message] || "Hello"
+options[:times].times { puts msg }

Ruby/fibonacci.rb

@@ -0,0 +1,10 @@
+# fibonacci.rb
+def fib(n)
+  a, b = 0, 1
+  n.times { a, b = b, a + b }
+  a
+end
+
+print "How many Fibonacci numbers? "
+m = gets.to_i
+(0...m).each { |i| puts "#{i}: #{fib(i)}" }

Ruby/shapes.rb

@@ -0,0 +1,16 @@
+# shapes.rb
+module Area
+  def area
+    raise NotImplementedError
+  end
+end
+
+class Rectangle
+  include Area
+  attr_reader :w, :h
+  def initialize(w, h); @w = w; @h = h; end
+  def area; w * h; end
+end
+
+r = Rectangle.new(3, 4)
+puts "Rectangle area = #{r.area}"