Improve 'SET' command

[drmarjanovic]

Summary:

• Separate Update (XX, NX, LT, GT) to Update (XX, NX) and UpdateByScore (LT, GT)
  • SET command only takes NX | XX (more info here)
  • ZADD command takes both NX | XX and LT | GT (more info here) Note: The GT, LT and NX options are mutually exclusive. (This has not been implemented)
• Removed setEx,setNx, and pSetEx commands because they were deprecated since version 2.6.12
• Merge KeepTtl and durations because SET command can't take both expireAt and keepTtl
• Merge getEx commands into one
• Adapted tests