Output proper HTML markup for markdown input

RDoc formatters process inline markup on a paragraph-by-paragraph basis.
If this is not done then embedded markup in that paragraph will not be
output correctly.

Now the paragraph's contents are joined into a single line before
processing which allows the formatter to generate the correct output.

Fixes #204

Author: drbrain

History.rdoc

@@ -20,6 +20,8 @@
   * `rdoc --pipe` output now contains <code></code> for markdown compliance.
   * RDoc no longer leaves emacs-style modelines in .txt, .md or .rd files.
     Bug #178 by Zachary Scott
+  * RDoc no longer puts raw markup in HTML output for markdown input.  Bug
+    #204 by Erik Hollensbe
 
 === 4.0.0 / 2013-02-24
 

lib/rdoc/markup/paragraph.rb

@@ -21,7 +21,7 @@ def text hard_break = ''
       else
         part
       end
-    end.join
+    end.join.gsub(/\r?\n/, ' ')
   end
 
 end

test/test_rdoc_markup_to_html.rb

@@ -256,7 +256,7 @@ def accept_paragraph_br
   end
 
   def accept_paragraph_break
-    assert_equal "\n<p>hello<br>\nworld</p>\n", @to.res.join
+    assert_equal "\n<p>hello<br> world</p>\n", @to.res.join
   end
 
   def accept_paragraph_i