fixed RDB url string
modified ListDBInstances to use baseRequest
moved Link type definition to generic.go file
added list flavors method
added method to retrieve flavor url by name
added MarshalJSON method for DatabaseReq
Added Security Group and Security Rules types
added git create instance method and created structs for instance response
added GetDBInstance to get instance details
added GetEndpointURL function
changed error to panic, fixed addressing in flavor ref
fixed errors with createDB and struct type mismatch
added delete instance function
added instance restart function
fixed server response type forCreateDB
fixed pointer
changed type to a struct in NewDB repsonse
changed type to a struct in NewDB repsonse