additional list functions
additional list functions

implements the following methods
 - Get(index int64) (string, error)
 - Size() (int64, error)
 - PopFirst() (string, error)
 - PopLast() (string, error)
 - AddStart(value string) error
 - AddEnd(value string) error
 - Add(value string) error
 - RemoveElement(value string) error
 - Set(index int64, value string) error
 - Trim(start, stop int64) error

xyproto/simpleredis