Merge branch develop into master

[GanZiheng]

Development Task

Merge develop into master part by part.

Development Progress

The pull requests merged at develop branch are as follows, I would try to apply them into master.

• vlog

  • #84 @zhangjinpeng1987 #143
  • #88 @zhangjinpeng1987 #127

• memtable

  • #45 @GanZiheng #126
  • #46 @GanZiheng #126

• levels

  • #47 @zhangjinpeng1987 #138
  • #50 @zhangjinpeng1987 #148
  • #52 @GanZiheng #129
  • #54 @GanZiheng #129
  • #75 @GanZiheng #129
  • #73 @GanZiheng #129
  • #77 @GanZiheng #129
  • #78 @GanZiheng #129
  • #101 @GanZiheng #129

• txn

  • #57 @GanZiheng #132
  • #67 @GanZiheng
    • #136
    • #143
  • #72 @GanZiheng #143

• agate

  • #58 @GanZiheng #127
  • #62 @GanZiheng #127
  • #60 @GanZiheng #123
  • #87 @GanZiheng #170
  • #91 @GanZiheng #170

• bench

  • #86 @GanZiheng #169
  • #90 @GanZiheng #169
  • #93 @GanZiheng #167
  • #94 @GanZiheng #167
  • #96 @GanZiheng #167
  • #99 @GanZiheng #167
  • #102 @GanZiheng #167

[GanZiheng]

@skyzh PTAL, thx.

[GanZiheng]

I think we may not need to apply these prs one by one. I would like to port Badger and create pr by module, such as levels, txn and so on.

[skyzh]

That's cool! I think it's also okay to port module by module. But sometimes, reviewers might not be knowing what some code is doing without looking ahead for future PRs. I'd be okay with any solution.