Add: %W flag for complete_bar_with_percentage

Why This Change Is Necessary
========================================================================

- [ ] Bug Fix
- [x] New Feature

Exposes already existing support for complete (full-length) progress bar
with integrated percentage.

Side Effects Caused By This Change
========================================================================

- [ ] This Causes a Breaking Change
- [x] This Does Not Cause Any Known Side Effects

Checklist
========================================================================

- [x] I have run `rubocop` against the codebase
- [x] I have added tests to cover my changes
- [x] All new and existing tests passed

------------------------------------------------------------------------
Github Issue URLs:
  * #146

lib/ruby-progressbar/components/bar.rb

@@ -57,7 +57,13 @@ def bar(length)
   def complete_bar(length)
     self.length = length
 
-    to_s
+    to_s(:format => :standard)
+  end
+
+  def complete_bar_with_percentage(length)
+    self.length = length
+
+    to_s(:format => :integrated_percentage)
   end
 
   def unknown_string

lib/ruby-progressbar/format/molecule.rb

@@ -17,13 +17,14 @@ class   Molecule
     :f => [:time,         :estimated_with_no_oob],
     :B => [:bar,          :complete_bar],
     :b => [:bar,          :bar],
+    :W => [:bar,          :complete_bar_with_percentage],
     :w => [:bar,          :bar_with_percentage],
     :i => [:bar,          :incomplete_space],
     :r => [:rate,         :rate_of_change],
     :R => [:rate,         :rate_of_change_with_precision]
   }.freeze
 
-  BAR_MOLECULES = %w{w B b i}.freeze
+  BAR_MOLECULES = %w{W w B b i}.freeze
 
   attr_accessor :key,
                 :method_name

spec/ruby-progressbar/format/formatter_spec.rb

@@ -619,6 +619,27 @@ module   Format
     end
   end
 
+  context 'the %W flag' do
+    let(:format) { Format::String.new('%W') }
+
+    it 'is the bar with percentage (including incomplete space)' do
+      progressbar = ProgressBar::Base.new(:length => 100)
+
+      expect(Formatter.process(format, 100, progressbar)).to eql ' ' * 100
+      4.times { progressbar.increment }
+      expect(Formatter.process(format, 100, progressbar)).to eql "====#{' ' * 96}"
+      progressbar.increment
+      expect(Formatter.process(format, 100, progressbar)).to eql "= 5 =#{' ' * 95}"
+      5.times { progressbar.increment }
+      expect(Formatter.process(format, 100, progressbar)).to eql "=== 10 ===#{' ' * 90}"
+      progressbar.decrement
+      expect(Formatter.process(format, 100, progressbar)).to eql "=== 9 ===#{' ' * 91}"
+      91.times { progressbar.increment }
+      expect(Formatter.process(format, 100, progressbar)).to eql \
+        "#{'=' * 47} 100 #{'=' * 48}"
+    end
+  end
+
   context 'the %w flag' do
     let(:format) { Format::String.new('%w') }