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/attributes/attributes.md

@@ -0,0 +1,57 @@
+This is a simple test for attributes
+*** Parameters: ***
+{}
+*** Markdown input: ***
+
+Header with attributes	{#header1}	
+----------------------
+
+### Header with attributes ###	{#header2}	
+
+### Header no attributes ###
+
+{:warn2}Paragraph with a.
+{#par1}
+
+Paragraph with *emphasis*{:hello notfound}
+   {#par2}
+
+{:hello: .chello}
+*** Output of inspect ***
+md_el(:document,[
+	md_el(:header,["Header with attributes"],{:level=>2},[[:id, "header1"]]),
+	md_el(:header,["Header with attributes"],{:level=>3},[[:id, "header2"]]),
+	md_el(:header,["Header no attributes"],{:level=>3},[]),
+	md_par(["Paragraph with a."], [[:id, "par1"]]),
+	md_par([
+		"Paragraph with ",
+		md_em(["emphasis"], [[:ref, "hello"], [:ref, "notfound"]])
+	], [[:id, "par2"]]),
+	md_el(:ald,[],{:ald=>[[:class, "chello"]],:ald_id=>"hello"},[])
+],{},[])
+*** Output of to_html ***
+<h2 id="header1">Header with attributes</h2>
+
+<h3 id="header2">Header with attributes</h3>
+
+<h3 id="header_no_attributes_3">Header no attributes</h3>
+
+<p id="par1">Paragraph with a.</p>
+
+<p id="par2">Paragraph with <em class="chello">emphasis</em></p>
+*** Output of to_latex ***
+\hypertarget{header1}{}\subsection*{{Header with attributes}}\label{header1}
+
+\hypertarget{header2}{}\subsubsection*{{Header with attributes}}\label{header2}
+
+\hypertarget{header_no_attributes_3}{}\subsubsection*{{Header no attributes}}\label{header_no_attributes_3}
+
+Paragraph with a.
+
+Paragraph with \emph{emphasis}
+*** Output of to_md ***
+Header with attributesHeader with attributesHeader no attributesParagraph with a.
+
+Paragraph with emphasis
+*** Output of to_s ***
+Header with attributesHeader with attributesHeader no attributesParagraph with a.Paragraph with emphasis