Feature option to change color theme

* Add `config.style` option, to allow use change render style.

lib/rucaptcha.rb

@@ -19,6 +19,7 @@ module RuCaptcha
       @config.implode     = 0.4
       @config.cache_limit = 100
       @config.expires_in  = 2.minutes
+      @config.style       = :colorful
       @config
     end
 

lib/rucaptcha/captcha.rb

@@ -3,8 +3,13 @@ require 'posix-spawn'
 module RuCaptcha
   class Captcha
     class << self
-      def rand_color
-        [rand(100).to_s(8), rand(100).to_s(8), rand(100).to_s(8)]
+      def random_color
+        if RuCaptcha.config.style == :colorful
+          [rand(100).to_s(8), rand(100).to_s(8), rand(100).to_s(8)]
+        else
+          color_seed = rand(50).to_s(8)
+          [color_seed, color_seed, color_seed]
+        end
       end
 
       def random_chars
@@ -37,7 +42,7 @@ module RuCaptcha
         text_opts = []
         line_opts = []
         chars.each_with_index do |char, i|
-          rgb = rand_color
+          rgb = random_color
           text_color = "rgba(#{rgb.join(',')}, 1)"
           line_color = "rgba(#{rgb.join(',')}, 0.6)"
           text_opts << %(-fill '#{text_color}' -draw 'text #{(text_left + text_width) * i + all_left},#{text_top} "#{char}"')

lib/rucaptcha/configuration.rb

@@ -11,6 +11,8 @@ module RuCaptcha
     # Number of Captcha codes limit
     # set 0 to disable limit and file cache, default: 100
     attr_accessor :cache_limit
+    # Color style, default: :colorful, allows: [:colorful, :black_white]
+    attr_accessor :style
     # session[:_rucaptcha] expire time, default 2 minutes
     attr_accessor :expires_in
   end

lib/rucaptcha/version.rb

@@ -1,3 +1,3 @@
 module RuCaptcha
-  VERSION = '0.3.3'
+  VERSION = '0.4.0'
 end