v0.5.4

Note that v0.5.3 was released and pulled back due to a bug.

What's Changed

• part: Allow reusing Txn after commit by @joamaki in #113
• part: Use atomic.Pointer for storing previous txn by @joamaki in #115
• part: Remove the unnecessary empty root node by @joamaki in #114
• statedb: Add TestDB_EmptyKeys by @joamaki in #118
• part: Compress tree on deletion by @joamaki in #117
• reconciler: Reuse incremental round state by @joamaki in #116
• part: Fix watch channels of demoted nodes by @joamaki in #119

Full Changelog: v0.5.2...v0.5.4