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
* 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
