0.20.0

Primary changes:

• Update to rxnetty 0.4.6, fixes metrics issue with client names in previous versions.
• Fix refresh of server list when using eureka.
• Added helper function for registering log4j2 appender after logging system has been configured (see #116).
• Switch to new nebula based build.

A comprehensive list of changes can be found in the commit log: v0.19.0...v0.20.0