Changed connection period to use less memory & changed reader/writer …

…to allow nil until being used (#497)

src/granite/connection_management.cr

@@ -4,12 +4,12 @@ module Granite::ConnectionManagement
     # database connection for read operations
     # all models use this value. Change it
     # to change it in all Granite::Base models.
-    class_property connection_switch_wait_period : Int64 = Granite::Connections.connection_switch_wait_period
+    class_property connection_switch_wait_period : Int32 = Granite::Connections.connection_switch_wait_period
     @@last_write_time = Time.monotonic
 
     class_property current_adapter : Granite::Adapter::Base?
-    class_property reader_adapter : Granite::Adapter::Base = Granite::Connections.first_reader
-    class_property writer_adapter : Granite::Adapter::Base = Granite::Connections.first_writer
+    class_property reader_adapter : Granite::Adapter::Base?
+    class_property writer_adapter : Granite::Adapter::Base?
 
     def self.last_write_time
       @@last_write_time

src/granite/connections.cr

@@ -1,6 +1,6 @@
 module Granite
   class Connections
-    class_property connection_switch_wait_period : Int64 = 2000
+    class_property connection_switch_wait_period : Int32 = 2000
     class_getter registered_connections = [] of {writer: Granite::Adapter::Base, reader: Granite::Adapter::Base}
 
     # Registers the given *adapter*.  Raises if an adapter with the same name has already been registered.