add more skeletons code for merge policy
add more config related code
enrich MergePolicy and SegmentInfoPerCommit
add more index writer and documents writer skeleton code
add TieredMergePolicy.SetXYZ() methods
implement lock.obtainWith()
implement SimpleFSLock and RAM lock
add LogDoMergePolicy constructor
check before message
add closing control to sync closing actions
implement RAMInputStream
workaround reentrant lock
implement MockDirectoryWrapper.openInput()
add more test
implement test's newField()