anchor.diff:  * Use index-prefix fields for terms of length min_chars - 1 {pull}36703[#36703]
   
   Recovery::
  +* Do not wait for advancement of checkpoint in recovery {pull}39006[#39006] (issues: {issue}38949[#38949], {issue}39000[#39000])
   * SyncedFlushService.getShardRoutingTable() should use metadata to check for index existence {pull}37691[#37691] (issue: {issue}33888[#33888])
   * Make prepare engine step of recovery source non-blocking {pull}37573[#37573] (issue: {issue}37174[#37174])
   * Make recovery source send operations non-blocking {pull}37503[#37503] (issue: {issue}37458[#37458])
  
positive.code: * Deprecate the low-level REST client on JDK 7 {pull}38542[#38542] (issue: {issue}29607[#29607])
  * Deprecate maxRetryTimeout in RestClient and increase default value {pull}38425[#38425] (issue: {issue}38085[#38085])
  
  Infra/Core::
  * Core: Deprecate negative epoch timestamps {pull}36793[#36793]
  
  Infra/REST API::
  * Deprecate requests that have an unconsumed body {pull}37534[#37534] (issue: {issue}37504[#37504])
  
negative.code: * Replaced the word 'shards' with 'replicas' in an error message. (#36234) {pull}36275[#36275] (issue: {issue}36234[#36234])
  
  Engine::
  * Bubble up exception when processing NoOp {pull}39338[#39338] (issue: {issue}38898[#38898])
  * ReadOnlyEngine should update translog recovery state information {pull}39238[#39238]
  * Advance max_seq_no before add operation to Lucene {pull}38879[#38879] (issue: {issue}31629[#31629])
  
  Features/Features::
  * Link to 7.0 documentation in deprecation checks {pull}39194[#39194]
  * Handle Null in FetchSourceContext#fetchSource {pull}36839[#36839] (issue: {issue}29293[#29293])
  
  Features/ILM::
  * Handle failure to release retention leases in ILM {pull}39281[#39281] (issue: {issue}39181[#39181])
  * Preserve ILM operation mode when creating new lifecycles {pull}38134[#38134] (issues: {issue}38229[#38229], {issue}38230[#38230])
  * Retry ILM steps that fail due to SnapshotInProgressException {pull}37624[#37624] (issues: {issue}37541[#37541], {issue}37552[#37552])
  * Remove `indexing_complete` when removing policy {pull}36620[#36620]
  