Release 1.19.0-incubating

This is the first of Apache Pulsar since entering the ASF incubator.

Major changes included in this release are:

• [#524] Moved APIs from com.yahoo.pulsar to org.apache.pulsar
• [#548] Added stateless Pulsar proxy
• [#538] Support for non-persistent topics
• [#587] Upgraded RocksDB to comply with ASF policy
• [#507] Instrumentation of ZooKeeper client to expose metrics
• Various fixes for TLS auth in WebSocket proxy

Complete list of changes can be found at:
https://github.com/apache/incubator-pulsar/milestone/8?closed=1