switch to discovery.status metric for eureka-avg (Netflix#1081)

Backport of Netflix#1039.

This is a newer version that avoids the need for regex and
follows current conventions.

fix build settings for 2.13 to use `-release 8` (Netflix#1055)

Before it was looking specifically for version 12. For now
we still need to be able to run on jdk8+. The specific issue
encountered was:

```
java.lang.NoSuchMethodError: java.nio.CharBuffer.clear()Ljava/nio/CharBuffer;
   at com.netflix.atlas.core.model.TaggedItem$.writePair(TaggedItem.scala:59)
   at com.netflix.atlas.core.model.TaggedItem$.computeId(TaggedItem.scala:105)
   at com.netflix.atlas.core.model.TimeSeries$.<clinit>(TimeSeries.scala:22)
   at com.netflix.atlas.core.model.EvalContext.<init>(EvalContext.scala:32)
   at com.netflix.atlas.druid.DruidDatabaseActorSuite.<init>(DruidDatabaseActorSuite.scala:259)
   at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
   at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
   at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
   at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
   at java.lang.Class.newInstance(Class.java:442)
```

Also improves the check for recent JDKs.

1.6: update to scala 2.13.0 final (Netflix#1053)

fix deprecation warnings for ActorPublisher (Netflix#1037)

Changes the processing for the `/fetch` endpoint to use
streams instead of the deprecated ActorPublisher.

1.5: switch to RobotoMono font (Netflix#1033)

Backport of Netflix#967 to get better behavior when running on
newer JDKs that do not include the Lucida fonts.

update dependencies (Netflix#947)

store step size for TimeGroup (Netflix#929)

If it is flushed via a heartbeat instead of data, then it
could be empty and the step size cannot be extracted from
the data.

make subscribe logs consistent with register (Netflix#897)

Only log on changes to reduce noise and follow the same
behavior as register/unregister.

add timeRange helper function (Netflix#859)

There are a number of internal libs that have this same
logic of computing a time range based on parsed start and
end times that can be relative to each other. Move to a
helper function of Strings so it is easier to reuse.

iep 1.2.2 (Netflix#815)

This is mostly just to trigger a change to verify the
release. The previous attempt at 1.6.0-rc.10 failed
because it was still trying to publish 1.6.0-rc.9. The
theory is that this is because they were both tagging
the same commit.