Remove the word middleware (#1067)

* 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

plugin/log/README.md

@@ -0,0 +1,102 @@
+# log
+
+*log* enables query logging to standard output.
+
+## Syntax
+
+~~~ txt
+log
+~~~
+
+* With no arguments, a query log entry is written to *stdout* in the common log format for all requests
+
+~~~ txt
+log FILE
+~~~
+
+* **FILE** is the log file to create (or append to). The *only* valid name for **FILE** is *stdout*.
+
+~~~ txt
+log [NAME] FILE [FORMAT]
+~~~
+
+* `NAME` is the name to match in order to be logged
+* `FILE` is the log file (again only *stdout* is allowed here).
+* `FORMAT` is the log format to use (default is Common Log Format)
+
+You can further specify the class of responses that get logged:
+
+~~~ txt
+log [NAME] FILE [FORMAT] {
+    class [success|denial|error|all]
+}
+~~~
+
+Here `success` `denial` and `error` denotes the class of responses that should be logged. The
+classes have the following meaning:
+
+* `success`: successful response
+* `denial`: either NXDOMAIN or NODATA (name exists, type does not)
+* `error`: SERVFAIL, NOTIMP, REFUSED, etc. Anything that indicates the remote server is not willing to
+    resolve the request.
+* `all`: the default - nothing is specified.
+
+If no class is specified, it defaults to *all*.
+
+## Log File
+
+The "log file" can only be *stdout*. CoreDNS expects another service to pick up this output and deal
+with it, i.e. journald when using systemd or Docker's logging capabilities.
+
+## Log Format
+
+You can specify a custom log format with any placeholder values. Log supports both request and
+response placeholders.
+
+The following place holders are supported:
+
+* `{type}`: qtype of the request
+* `{name}`: qname of the request
+* `{class}`: qclass of the request
+* `{proto}`: protocol used (tcp or udp)
+* `{when}`: time of the query
+* `{remote}`: client's IP address
+* `{size}`: request size in bytes
+* `{port}`: client's port
+* `{duration}`: response duration
+* `{rcode}`: response RCODE
+* `{rsize}`: response size
+* `{>rflags}`: response flags, each set flag will be displayed, e.g. "aa, tc". This includes the qr
+  bit as well.
+* `{>bufsize}`: the EDNS0 buffer size advertised in the query
+* `{>do}`: is the EDNS0 DO (DNSSEC OK) bit set in the query
+* `{>id}`: query ID
+* `{>opcode}`: query OPCODE
+
+The default Common Log Format is:
+
+~~~ txt
+`{remote} - [{when}] "{type} {class} {name} {proto} {size} {>do} {>bufsize}" {rcode} {>rflags} {rsize} {duration}`
+~~~
+
+## Examples
+
+Log all requests to stdout
+
+~~~
+log stdout
+~~~
+
+Custom log format, for all zones (`.`)
+
+~~~
+log . stdout "{proto} Request: {name} {type} {>id}"
+~~~
+
+Only log denials for example.org (and below to a file)
+
+~~~
+log example.org stdout {
+    class denial
+}
+~~~