don't warn if ANSICON not installed on Windows. Document ANSICON utils for Windows in colors.feature

issue #2020
don't need to test if ANSICON installed on windows (that's up to the user; ok if it isn't)
document Windows utils available for showing color (ex: ANSICON and other solutions)
moved 'Windows may need solutions to show ANSI codes' into its own feature file.  Massaged text to it can stand alone.
added new 'color.feature' file into .nav file after 'read_options_from_file.feature' (in configuration section)
replaced color= method with attr_writer :color; fixed typo in color.feature. Added link to wikipedia definition for ANSI escape code in color.feature

Author: weedySeaDragon

features/.nav

@@ -40,6 +40,7 @@
   - run_all_when_everything_filtered.feature
 - configuration:
   - read_options_from_file.feature
+  - color.feature
   - fail_fast.feature
   - custom_settings.feature
   - alias_example_to.feature

features/configuration/color.feature

@@ -0,0 +1,22 @@
+Feature: Windows may require additional solutions to display color
+
+  The output uses [ANSI escape codes](https://en.wikipedia.org/wiki/ANSI_escape_code) to show text in color.  Windows
+  systems (shells) often don't interpret those codes at all.
+
+  If you're on Windows and you see ANSI escape codes in the output
+  (something like `[1m [31m` ) and your text isn't in different colors,
+  you may need to install a utility so that your Windows shell will
+  interpret those codes correctly and show the colors.  Here are some
+  popular solutions:
+
+    * [ANSICON](https://github.com/adoxa/ansicon): ANSICON runs 'on top of' cmd or powershell. This is a very
+      popular solution. You can set it up so that it's always used whenever
+      you use cmd or powershell, or use it only at specific times.
+
+    * Alternatives to cmd.exe or powershell: [ConEmu](http://conemu.github.io/), [Console2](http://sourceforge.net/projects/console/),
+      [ConsoleZ](https://github.com/cbucher/console)
+
+    * Unix-like shells and utilities:  [cygwin](https://www.cygwin.com/), [babun](http://babun.github.io/index.html),
+      [MinGW](http://www.mingw.org/) (Minimalist GNU for Windows)
+
+  To find out more, search for information about those solutions.

lib/rspec/core/configuration.rb

@@ -695,9 +695,7 @@ def full_backtrace=(true_or_false)
       #
       # @see color_enabled?
       # @return [Boolean]
-      def color
-        value_for(:color) { @color }
-      end
+      attr_writer :color
 
       # Check if color is enabled for a particular output.
       # @param output [IO] an output stream to use, defaults to the current
@@ -711,15 +709,7 @@ def color_enabled?(output=output_stream)
       # @attr true_or_false [Boolean] toggle color enabled
       def color=(true_or_false)
         return unless true_or_false
-
-        if RSpec::Support::OS.windows? && !ENV['ANSICON']
-          RSpec.warning "You must use ANSICON 1.31 or later " \
-                        "(http://adoxa.3eeweb.com/ansicon/) to use colour " \
-                        "on Windows"
-          @color = false
-        else
-          @color = true
-        end
+        @color = !!true_or_false
       end
 
       # @private

spec/rspec/core/configuration_spec.rb

@@ -1156,58 +1156,6 @@ def metadata_hash(*args)
         end
       end
 
-      context "on windows" do
-        before do
-          @original_host  = RbConfig::CONFIG['host_os']
-          RbConfig::CONFIG['host_os'] = 'mingw'
-          allow(config).to receive(:require)
-        end
-
-        after do
-          RbConfig::CONFIG['host_os'] = @original_host
-        end
-
-        context "with ANSICON available" do
-          around(:each) { |e| with_env_vars('ANSICON' => 'ANSICON', &e) }
-
-          it "enables colors" do
-            config.output_stream = StringIO.new
-            allow(config.output_stream).to receive_messages :tty? => true
-            config.color = true
-            expect(config.color).to be_truthy
-          end
-
-          it "leaves output stream intact" do
-            config.output_stream = $stdout
-            allow(config).to receive(:require) do |what|
-              config.output_stream = 'foo' if what =~ /Win32/
-            end
-            config.color = true
-            expect(config.output_stream).to eq($stdout)
-          end
-        end
-
-        context "with ANSICON NOT available" do
-          around { |e| without_env_vars('ANSICON', &e) }
-
-          before do
-            allow_warning
-          end
-
-          it "warns to install ANSICON" do
-            allow(config).to receive(:require) { raise LoadError }
-            expect_warning_with_call_site(__FILE__, __LINE__ + 1, /You must use ANSICON/)
-            config.color = true
-          end
-
-          it "sets color to false" do
-            allow(config).to receive(:require) { raise LoadError }
-            config.color = true
-            expect(config.color).to be_falsey
-          end
-        end
-      end
-
       it "prefers incoming cli_args" do
         config.output_stream = StringIO.new
         allow(config.output_stream).to receive_messages :tty? => true