Add Authentication documentation & simplify interface

Author: dCSeven

README.rdoc

@@ -1,6 +1,5 @@
 
-    Em-mongo is no longer being maintained (hasn't been for some time). If you are interested in the commit bit
-    or want to take over the full project, please let me know!
+    Em-mongo needs collaborators to help maintaining this project. If you are interested, please let me know!
 
 = EM-Mongo
 
@@ -122,6 +121,22 @@ In addition to calling your errback if the write fails, you can provide the usua
 
   safe_insert( {:a=>"v"}, :last_error_params => { :fsync => true, :w => 5 } )
 
+
+== Authentication
+At the moment the mechhanisms SCRAM-SHA-1(:scram_sha1) and MONGODB-CR(:mongodb_cr) are supported.
+It works as follows:
+
+    # establish connection and get authentication db
+    connection = EM::Mongo::Connection.new(db_server, port)
+    auth_db = connection.db(db_name)
+    
+    # authentication itself
+    resp = auth_db.authenticate(user,password, :scram_sha1)
+    resp.callback do |success| 
+      do_authenticated #auth successful
+    end
+    resp.errback {|err| auth_failure err} # authentication failed
+
 == Documentation
 
 em-mongo now has some YARD docs. These are mostly ported directly from the mongo-ruby-driver. While they have been updated to reflect em-mongo's async API, there are probably a few errors left over in the translation. Please file an issue or submit a pull request if you notice any inaccuracies. 

lib/em-mongo/auth/mongodb_cr.rb

@@ -12,7 +12,9 @@ def authenticate(username, password)
       auth_resp = @db.collection(SYSTEM_COMMAND_COLLECTION).first({'getnonce' => 1})
       auth_resp.callback do |res|
         if not res or not res['nonce']
-          response.succeed false
+          if res.nil? then response.fail "connection failure"
+          else response.fail "invalid first server response: " + res.to_s
+          end
         else
           auth                 = BSON::OrderedHash.new
           auth['authenticate'] = 1