DLedger-0.2.4

This release fixes some bugs and support multi-dirs storage

Feature

#119 Support multi-dirs storage

Bug

#123 Fix high CPU in EntryDispatcher
#89 DLedgerMmapFileStore move flushedWhere pos after truncate file
#106 Fix preferred leader bug

Enhancement

#112 It is better for the peer with the smallest lag(fall behind index) to become the transferee.
#110 Use df algorithm to calculate the disk used ratio
#117 Some class's method lost annotation 'Override'
#104 The variable DLedgerMmapFileStore#isDiskFull should be decorated with the volatile.
#115 Bump junit to 5.8.2
#121 Fix check style error