Add br tag for documentation.

This tag allows for a simple linefeed in a p tag instead of being forced to start a new paragraph.

doc/lib/pgBackRestDoc/Common/DocRender.pm

@@ -31,6 +31,7 @@ my $oRenderTag =
 {
     'markdown' =>
     {
+        'br' => ['\n', ''],
         'quote' => ['"', '"'],
         'b' => ['**', '**'],
         'i' => ['_', '_'],
@@ -55,6 +56,7 @@ my $oRenderTag =
 
     'text' =>
     {
+        'br' => ['\n', ''],
         'quote' => ['"', '"'],
         'p' => ['', "\n\n"],
         'b' => ['', ''],
@@ -82,6 +84,7 @@ my $oRenderTag =
 
     'latex' =>
     {
+        'br' => ['\\\vspace{1em}', ''],
         'quote' => ['``', '"'],
         'p' => ["\n\\begin{sloppypar}", "\\end{sloppypar}\n"],
         'b' => ['\textbf{', '}'],
@@ -115,6 +118,7 @@ my $oRenderTag =
 
     'html' =>
     {
+        'br' => ['<br/>', ''],
         'quote' => ['<q>', '</q>'],
         'b' => ['<b>', '</b>'],
         'i' => ['<i>', '</i>'],

doc/xml/dtd/doc.dtd

@@ -237,9 +237,10 @@
                    br-setting|pg-option|pg-setting|link|user|proper)*>
 <!ELEMENT p ANY>
     <!ATTLIST p if CDATA "">
-<!ELEMENT text (p|list|admonition)*>
+<!ELEMENT text (p|list|admonition|br)*>
 <!ELEMENT i ANY>
 <!ELEMENT b ANY>
+<!ELEMENT br ANY>
 <!ELEMENT list (list-item+)>
     <!ATTLIST list if CDATA "">
 <!ELEMENT list-item ANY>