doc: make -f Makefile.doc (#2919)

mechanical change: create the manual pages.

Signed-off-by: Miek Gieben <miek@miek.nl>

man/coredns-metadata.7

@@ -1,11 +1,11 @@
 .\" Generated by Mmark Markdown Processer - mmark.nl
-.TH "COREDNS-METADATA" "7" "April 2019" "CoreDNS" "CoreDNS Plugins"
+.TH "COREDNS-METADATA" 7 "June 2019" "CoreDNS" "CoreDNS Plugins"
 
-.SH NAME
+.SH "NAME"
 .PP
 \fImetadata\fP - enable a meta data collector.
 
-.SH DESCRIPTION
+.SH "DESCRIPTION"
 .PP
 By enabling \fImetadata\fP any plugin that implements metadata.Provider
 interface
@@ -28,7 +28,7 @@ plugin enforces is that the labels contains a slash. See the documentation for
 The value stored is a string. The empty string signals "no meta data". See the documentation for
 \fB\fCmetadata.ValueFunc\fR on how to retrieve this.
 
-.SH SYNTAX
+.SH "SYNTAX"
 .PP
 .RS
 
@@ -42,7 +42,7 @@ metadata [ZONES... ]
 \fBZONES\fP zones metadata should be invoked for.
 
 
-.SH PLUGINS
+.SH "PLUGINS"
 .PP
 \fB\fCmetadata.Provider\fR interface needs to be implemented by each plugin willing to provide metadata
 information for other plugins. It will be called by metadata and gather the information from all
@@ -51,11 +51,11 @@ plugins in context.
 .PP
 Note: this method should work quickly, because it is called for every request.
 
-.SH EXAMPLES
+.SH "EXAMPLES"
 .PP
 The \fIrewrite\fP plugin uses meta data to rewrite requests.
 
-.SH ALSO SEE
+.SH "ALSO SEE"
 .PP
 The Provider interface
 \[la]https://godoc.org/github.com/coredns/coredns/plugin/metadata#Provider\[ra] and