REXML is dead. Long live Nokogiri.

Modify Maruku to use Nokogiri instead of REXML.
Produces a 3-fold speedup in the #to_html method.

vendor/plugins/maruku/spec/block_docs/xml_instruction.md

@@ -0,0 +1,52 @@
+Directives should be preserved.
+*** Parameters: ***
+{}
+*** Markdown input: ***
+
+<? noTarget?> 
+<?php ?> 
+<?xml ?> 
+<?mrk ?>
+
+Targets <? noTarget?> <?php ?> <?xml ?> <?mrk ?>
+
+Inside: <?mrk puts "Inside: Hello" ?> last
+
+
+*** Output of inspect ***
+md_el(:document,[
+	md_el(:xml_instr,[],{:code=>" noTarget",:target=>""},[]),
+	md_el(:xml_instr,[],{:code=>"",:target=>"php"},[]),
+	md_el(:xml_instr,[],{:code=>"",:target=>"xml"},[]),
+	md_el(:xml_instr,[],{:code=>"",:target=>"mrk"},[]),
+	md_par([
+		"Targets ",
+		md_el(:xml_instr,[],{:code=>"noTarget",:target=>""},[]),
+		" ",
+		md_el(:xml_instr,[],{:code=>"",:target=>"php"},[]),
+		" ",
+		md_el(:xml_instr,[],{:code=>"",:target=>"xml"},[]),
+		" ",
+		md_el(:xml_instr,[],{:code=>"",:target=>"mrk"},[])
+	]),
+	md_par([
+		"Inside: ",
+		md_el(:xml_instr,[],{:code=>"puts \"Inside: Hello\"",:target=>"mrk"},[]),
+		" last"
+	])
+],{},[])
+*** Output of to_html ***
+<?  noTarget?><?php ?><?xml ?><?mrk ?>
+<p>Targets <? noTarget?> <?php ?> <?xml ?> <?mrk ?></p>
+
+<p>Inside: <?mrk puts "Inside: Hello"?> last</p>
+*** Output of to_latex ***
+Targets    
+
+Inside:  last
+*** Output of to_md ***
+Targets
+
+Inside: last
+*** Output of to_s ***
+Targets    Inside:  last