Started the refactoring work on couchrest.

* A server can have multiple defined available databases set to be used by documents (think DM repos)
* A server can have a default database so documents can easily share the same db connection
* Let a document class have a default database to use
* Give access to a document uri
* extracted some of the document features to a mixin

lib/couchrest/core/server.rb

@@ -1,25 +1,62 @@
 module CouchRest
   class Server
-    attr_accessor :uri, :uuid_batch_count
-    def initialize server = 'http://127.0.0.1:5984', uuid_batch_count = 1000
+    attr_accessor :uri, :uuid_batch_count, :available_databases
+    def initialize(server = 'http://127.0.0.1:5984', uuid_batch_count = 1000)
       @uri = server
       @uuid_batch_count = uuid_batch_count
     end
   
-    # List all databases on the server
+    # Lists all "available" databases.
+    # An available database, is a database that was specified
+    # as avaiable by your code.
+    # It allows to define common databases to use and reuse in your code
+    def available_databases
+      @available_databases ||= {}
+    end
+    
+    # Adds a new available database and create it unless it already exists
+    #
+    # Example:
+    #
+    # @couch = CouchRest::Server.new
+    # @couch.define_available_database(:default, "tech-blog")
+    #
+    def define_available_database(reference, db_name, create_unless_exists = true)
+      available_databases[reference.to_sym] = create_unless_exists ? database!(db_name) : database(db_name)
+    end
+  
+    # Checks that a database is set as available
+    #
+    # Example:
+    #
+    # @couch.available_database?(:default)
+    #
+    def available_database?(ref_or_name)
+      ref_or_name.is_a?(Symbol) ? available_databases.keys.include?(ref_or_name) : available_databases.values.map{|db| db.name}.include?(ref_or_name)
+    end
+  
+    def default_database=(name, create_unless_exists = true)
+      define_available_database(:default, name, create_unless_exists = true)
+    end
+    
+    def default_database
+      available_databases[:default]
+    end
+  
+    # Lists all databases on the server
     def databases
       CouchRest.get "#{@uri}/_all_dbs"
     end
   
     # Returns a CouchRest::Database for the given name
-    def database name
+    def database(name)
       CouchRest::Database.new(self, name)
     end
   
     # Creates the database if it doesn't exist
-    def database! name
+    def database!(name)
       create_db(name) rescue nil
-      database name
+      database(name)
     end
   
     # GET the welcome message
@@ -28,9 +65,9 @@ module CouchRest
     end
 
     # Create a database
-    def create_db name
+    def create_db(name)
       CouchRest.put "#{@uri}/#{name}"
-      database name
+      database(name)
     end
 
     # Restart the CouchDB instance
@@ -39,7 +76,7 @@ module CouchRest
     end
 
     # Retrive an unused UUID from CouchDB. Server instances manage caching a list of unused UUIDs.
-    def next_uuid count = @uuid_batch_count
+    def next_uuid(count = @uuid_batch_count)
       @uuids ||= []
       if @uuids.empty?
         @uuids = CouchRest.post("#{@uri}/_uuids?count=#{count}")["uuids"]