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/table_attributes.md

@@ -0,0 +1,34 @@
+Write a comment here
+*** Parameters: ***
+{} # params 
+*** Markdown input: ***
+
+h         | h
+----------|--
+{:t}  c1  | c2
+{: summary="Table summary" .class1 style="color:red" border=3 width="50%" frame=lhs rules=cols  cellspacing=2em cellpadding=4px}
+
+{:t: scope="row"}
+*** Output of inspect ***
+md_el(:document,[
+	md_el(:table,[
+		md_el(:head_cell,["h"],{},[]),
+		md_el(:head_cell,["h"],{},[]),
+		md_el(:cell,[" c1"],{},[[:ref, "t"]]),
+		md_el(:cell,["c2"],{},[])
+	],{:align=>[:left, :left]},[["summary", "Table summary"], [:class, "class1"], ["style", "color:red"], ["border", "3"], ["width", "50%"], ["frame", "lhs"], ["rules", "cols"], ["cellspacing", "2em"], ["cellpadding", "4px"]]),
+	md_el(:ald,[],{:ald=>[["scope", "row"]],:ald_id=>"t"},[])
+],{},[])
+*** Output of to_html ***
+<table class="class1" style="color:red" summary="Table summary" width="50%" frame="lhs" rules="cols" border="3" cellspacing="2em" cellpadding="4px"><thead><tr><th>h</th><th>h</th></tr></thead><tbody><tr><th scope="row" style="text-align: left;"> c1</th><td style="text-align: left;">c2</td>
+</tr></tbody></table>
+*** Output of to_latex ***
+\begin{tabular}{l|l}
+h&h\\
+\hline 
+ c1&c2\\
+\end{tabular}
+*** Output of to_md ***
+hh c1c2
+*** Output of to_s ***
+hh c1c2