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Port 2021 07 04

See merge request !1

reduce allocations

Fix CI

* Document how to get all entries in ranger
* update doc + test

* Add Len() to Ranger

* Update travis resiliency

##Summary
Investigated memory leak symptoms reported in #15 , and turns out path compression upon removal of networks was not implemented correctly, instead, it simply did a parent child reassignment.

Added to unit testing to prove desired behavior and added a memory leak unit test using a slightly modified version of the test used to uncover the problem in #15 , use -short flag in local testing to skip added slow test, as documented by https://golang.org/pkg/testing/#Short

Fixes errors produced by dep 0.5.0

Recent version of dep - 0.5.0 produces errors on `dep status`:
```
◦ dep status
Gopkg.lock is out of sync with imports and/or Gopkg.toml. Run `dep check` for details.
PROJECT  MISSING PACKAGES
input-digest mismatch
```

This commit updates `Gopkg.lock` to recent dep format

I essentially ran `dep ensure`.

Add CoveredNetworks option

This would cause error when checking out with git clone --recursive,
such as when golang dep clones the repo.
Signed-off-by: Rob Adams <readams@readams.net>

Signed-off-by: Rob Adams <readams@readams.net>

* Search by CIDR rather than just by IP.
Signed-off-by: Rob Adams <readams@readams.net>

travis: add 1.9.x to go versions

Fix index-out-of-bound bug when inserting network that shares direct branch point with single-IP (leaf) network, closes #3