re-enable doc artifacts (Netflix#1271)

They were disabled due to a bug, but looks like it
has been fixed. Fixed a number of scaladoc errors
to get the build clean.

Error from publishing attempt without docs:

```
Failed: javadoc-staging, failureMessage:Missing: no javadoc
  jar found in folder
  '/com/netflix/atlas_v1/atlas-module-lwcapi_2.13/1.7.0-rc.14'
```

add topk/bottomk that aggregates others (Netflix#1248)

Fixes Netflix#1224.

Adds variants of topk/bottomk that in addition to computing
the highest priority values will also return an aggregate
time series that includes all of the other time series that
were not high enough priority. This can be useful to see
what proportion of the overall volume is represented by
the highest priority time series. The operators have the
same signature as `:topk` and `:bottomk`, but the
aggregation to use is specified in the operator name.
There are four aggregates supported:

- min
- max
- sum
- avg

Count was not included as an aggregate because it could be
ambiguous and does not seem useful.

As part of this work there was some refactoring of the
existing aggregation operations to make the count case
more consistent.

eval: use BroadcastHub instead of Publisher (Netflix#1217)

Updates the queue source used for writing diagnostic
messages to use a BroadcastHub instead of Publisher.
The main reason is that under newer versions of akka
there is a 5s subscription timeout for the underlying
FanoutProcessor created with the Publisher.

All other users of `asPublisher` were also converted
unless the `Publisher` type was explicitly needed as
part of the public API for the method.

quote special double values for all json formats (Netflix#1213)

Updates the `json` and `stats.json` formats to output
standard json data. Before special double values like
NaN and Infinity were emitted without qoutes breaking
some systems that expected standard json. This should
make them more straightforward to consume, however it
is a potentially breaking change for some users.

Fixes Netflix#1080

include tags in validation result responses (Netflix#1203)

Metrics are typically submitted in large batches and
without this context it can be difficult for users to
narrow it down to particular data points that are
problematic.

Sample of updated response:

```json
{
  "type": "partial",
  "errorCount": 1,
  "message": [
    "invalid characters in value: name = [answerTo Everything] ([--.0-9A-Z^_a-z~] are allowed) (tags={\"nf.node\":\"i-123\",\"atlas.dstype\":\"gauge\",\"name\":\"answerTo Everything\"})"
  ]
}
```

Fixes Netflix#1199

reduce allocations for asJavaMap.entrySet (Netflix#1197)

Updates the `SmallHashMap.asJavaMap` implementation to
override `entrySet()`. The new implementation avoids
allocations for each item in the map.

**Throughput**

| Benchmark            |        Before |         After | % Delta |
|----------------------|---------------|---------------|---------|
| customEntrySet       |   8,400,934.3 |  13,480,190.3 |    60.5 |

**Allocations**

| Benchmark            |        Before |         After | % Delta |
|----------------------|---------------|---------------|---------|
| customEntrySet       |         296.0 |          24.0 |   -91.9 |

1.6: update dependencies (Netflix#1187)

use jdk14 for travis build (Netflix#1174)

OpenJDK14 has changes to font rendering that make it
compatible with the lastest Zulu JDK11 we use internally.

update to latest jackson version (Netflix#1172)

Update to latest jackson version to pick up security
fixes.

atlas-eval: fix eval flow failure on lwc instance removal (Netflix#1165)

Currently the whole eval flow may fail when a lwc instance is
removed. There's a subflow for lwc api call of each lwc instance,
and that subflow is wrapped around by "RestartFlow" to enable
auto-retry. The subflow is finished from upstream when a lwc
instance is removed, and upstream of RestartFlow is finished,
RestartFlow finishes and propagate the failure from the current
ongoing attempt if any, to downstream, and eventually propagate
to main flow.

The fix is to have downstream of RestartFlow suppress the failure,
since the failure is expected and can be ignored on lwc instance
removal.