Remove optional dependencies

produce stats as part of rendering

since it was only introduced to because producing stats would hit the
renderer twice, which is no longer the case.

step 2 (and final step) in producing stats as part of Rendering

...so there is no need for a separate Stats method.

step 1: return stats from Render

Optimisation: replace three map-reduces with Renderers

This shows a big improvement in BenchmarkTopologyList

New type joinResult is created to hold the nodes and ID mapping.
The implementation move from host.go to render.go.

Pass 'id' through to the create function and expect that the result Node has that ID.
Extract a function newPseudoNode for common calls.

This is much more efficient as we skip creating then merging all intermediate Nodes

This means we are no longer generating a Counter for the number of
endpoint sub-nodes, but it seems that data was not used.

This is much more efficient as we skip creating then merging all intermediate Nodes

This allows us to avoid creating a host of 'IP' type Nodes then
discarding them after matching; instead we match directly and create
just the result we want.

To time a single topology, for more focused optimisation

Humanize reported durations

remove unused memoisation

Fixes #2923

Avoid object creation when scanning DNS names

We do this here rather than in ConnectionJoin since that way it is
obvious that the renderer isn't memoised already.

and add a comment indicating non-memoisation of other, not shared
top-level renderers.

This memoisation is effective when the browser requests multiple
topologies for the same report.

This deals with browsers requesting the same rendering for the same
timespan when no new reports have been received for that timespan.

we will re-introduce it more selectively later

Don't de-reference pointers from AWS without checking

Since we do this a lot, scanning the lists in-place saves time.
Also we don't need to sort them since StringSet is implemented as a
sorted set of strings

Simplify Utsname string conversion

Use Utsname from golang.org/x/sys/unix which contains byte array
instead of int8/uint8 array members. This allows to simplify the string
conversions of these members and the marshal.FromUtsname functions are
no longer needed.

MAINTAINER is deprecated, now using LABEL