Remove clear_all method and add comments to clear_all rake task

Author: taranda

README.md

@@ -95,17 +95,16 @@ CriticalPathCss.generate_all           # Generates critical CSS for all routes i
 CriticalPathCss.clear route            # Removes the CSS for the given route from the cache
 
 CriticalPathCss.clear_matched routes   # Removes the CSS for the matched routes from the cache
-
-CriticalPathCss.clear_all              # Clears all CSS from the cache
 ```
 
+NOTE: The `clear_matched` method will not work with Memcached due to the latter's incompatibility with Rails' `delete_matched` method.  We recommend using an alternative cache such as [Redis](https://github.com/redis-store/redis-rails).
+
 In addition to the `critical_path_css:generate` rake task described above, you also have access to task which clears the CSS cache:
 
 ```
 rake critical_path_css:clear_all
 ```
-
-NOTE: The `clear_all` and `clear_matched` methods will not work with Memcached due to the latter's incompatibility with Rails' `delete_matched` method.  We recommend using an alternative cache such as [Redis](https://github.com/redis-store/redis-rails).
+NOTE: The `critical_path_css:clear_all` rake task may need to be customized to suit your particular cache implementation.
 
 Careful use of these methods allows the developer to generate critical path CSS dynamically within the app.  The user should strongly consider using a [background job](http://edgeguides.rubyonrails.org/active_job_basics.html) when generating CSS in order to avoid tying up a rails thread.  The `generate` method will send a GET request to your server which could cause infinite recursion if the developer is not careful.
 

lib/critical-path-css-rails.rb

@@ -22,10 +22,6 @@ def self.clear_matched(routes)
     Rails.cache.delete_matched(routes,namespace: CACHE_NAMESPACE)
   end
 
-  def self.clear_all
-    self.clear_matched('*')
-  end
-
   def self.fetch(route)
     Rails.cache.read(route, namespace: CACHE_NAMESPACE) || ''
   end

lib/tasks/critical_path_css.rake

@@ -7,7 +7,10 @@ namespace :critical_path_css do
   end
   desc 'Clear all critical CSS from the cache'
   task clear_all: :environment do
-  	CriticalPathCss.clear_all
+  	# Use the following for Redis cache implmentations
+  	CriticalPathCss.clear_matched('*')
+  	# Some other cache implementations may require the following syntax instead
+  	# CriticalPathCss.clear_matched(/.*/)
   end
 end