docs: Regenerate all manpages using mmark (#2762)

Mmark recently became able to create manual pages. This removed the
dependency on 'ronn' and just uses mmark (Go program).

Re-hookup Makefile.doc to generate the correct header mmark needs to
see and regenate them all.

Spot checking a few pages suggest they look good and actually better
than rendered with ronn, esp. lists in lists.

Fixes #2757

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

man/coredns-root.7

@@ -1,40 +1,44 @@
-.\" generated with Ronn/v0.7.3
-.\" http://github.com/rtomayko/ronn/tree/0.7.3
-.
-.TH "COREDNS\-ROOT" "7" "March 2019" "CoreDNS" "CoreDNS plugins"
-.
-.SH "NAME"
-\fIroot\fR \- simply specifies the root of where to find (zone) files\.
-.
-.SH "DESCRIPTION"
-The default root is the current working directory of CoreDNS\. The \fIroot\fR plugin allows you to change this\. A relative root path is relative to the current working directory\.
-.
-.P
-This plugin can only be used once per Server Block\.
-.
-.SH "SYNTAX"
-.
-.nf
+.\" Generated by Mmark Markdown Processer - mmark.nl
+.TH "COREDNS-ROOT" "7" "April 2019" "CoreDNS" "CoreDNS Plugins"
 
+.SH ROOT
+.SH NAME
+.PP
+\fIroot\fP - simply specifies the root of where to find (zone) files.
+
+.SH DESCRIPTION
+.PP
+The default root is the current working directory of CoreDNS. The \fIroot\fP plugin allows you to change
+this. A relative root path is relative to the current working directory.
+
+.PP
+This plugin can only be used once per Server Block.
+
+.SH SYNTAX
+.PP
+.RS
+
+.nf
 root PATH
-.
-.fi
-.
-.P
-\fBPATH\fR is the directory to set as CoreDNS\' root\.
-.
-.SH "EXAMPLES"
-Serve zone data (when the \fIfile\fR plugin is used) from \fB/etc/coredns/zones\fR:
-.
-.IP "" 4
-.
-.nf
 
-\&\. {
+.fi
+.RE
+
+.PP
+\fBPATH\fP is the directory to set as CoreDNS' root.
+
+.SH EXAMPLES
+.PP
+Serve zone data (when the \fIfile\fP plugin is used) from \fB\fC/etc/coredns/zones\fR:
+
+.PP
+.RS
+
+.nf
+\&. {
     root /etc/coredns/zones
 }
-.
-.fi
-.
-.IP "" 0
+
+.fi
+.RE