If external plugins wanted to extend metrics there was no way since
zoneNames couldn't be initialized. Now plugins can call New to get an
instance of Metrics that they can extend.
We support ENV variables in config files, add an example in the one for
metric, note that `localhost:` is a valid host (in Go), so the
TestReadme will parse this correctly.
Fixes#1150
* doc update
Go through all README and fix mistakes, extend example and let more
corefile snippets be test for validity.
* Cant use spefic addr in test
Add a full test server impl in this new package + tests. Move
dnsrecorder into this package as well and finish up the commented out
tests that were left in the old dnsrecorder package.
Update all callers and tests.
* Rename middleware to plugin
first pass; mostly used 'sed', few spots where I manually changed
text.
This still builds a coredns binary.
* fmt error
* Rename AddMiddleware to AddPlugin
* Readd AddMiddleware to remain backwards compat
