0.8.0

Breaking

• [breaking] Changed format of block handles to store the last key of
  each block
• [breaking] Move Tree level_ratio from persisted to ephemeral config
• [perf] Improve point read performance
• [feat] Added ::new Constructor to STCS compaction strategy
• [perf] Use binary search during point reads to find segments inside disjoint levels
• [misc] Added benchmark
• [misc] Added more tests
• [misc] Internal refactors