concat-v1.6

Release notes:

• Directory extensions for manifest lookup [PR #125]
• Peer discovery through DHT rendezvous [PR #128]
• mcid usabililty improvements [PR #124]
• Statement DB vacuum support [PR #130]
• Misc fixes and improvements
  • version command for binaries [PR #122]
  • Add LIMIT clause to MCQL DELETE [PR #129]
  • Update rocksdb, disable concurrent memtable writing which is no longer supported with point lookup optimizations [PR #126]