Add support for ruby elements

Closes GH-47.

Author: wooorm

lib/handlers/index.js

@@ -90,6 +90,12 @@ exports.nobr = all
 exports.noscript = all
 exports.output = all
 exports.progress = all
+exports.rb = all
+exports.rbc = all
+exports.rp = all
+exports.rt = all
+exports.rtc = all
+exports.ruby = all
 exports.slot = all
 exports.small = all
 exports.span = all

test/fixtures/ruby-rt-rp-rbc-rtc-rb/index.html

@@ -0,0 +1,12 @@
+<p>The <code>&ltruby></code>, <code>&ltrt></code>, and <code>&ltrp></code> elements:</p>
+<p>
+  <ruby>漢<rp>（</rp><rt>かん</rt><rp>）</rp>字<rp>（</rp><rt>じ</rt><rp>）</rp></ruby>
+</p>
+<p>The legacy <code>&lt;rbc></code>, <code>&lt;rtc></code> and <code>&lt;rb></code> elements:</p>
+<p>
+  <ruby>
+    <rbc><rb>10</rb><rb>31</rb><rb>2002</rb></rbc>
+    <rtc><rt>Month</rt><rt>Day</rt><rt>Year</rt></rtc>
+    <rtc><rt rbspan="3">Expiration Date</rt></rtc>
+  </ruby>
+</p>

test/fixtures/ruby-rt-rp-rbc-rtc-rb/index.json

@@ -0,0 +1,3 @@
+{
+  "fragment": true
+}

test/fixtures/ruby-rt-rp-rbc-rtc-rb/index.md

@@ -0,0 +1,7 @@
+The `<ruby>`, `<rt>`, and `<rp>` elements:
+
+漢（かん）字（じ）
+
+The legacy `<rbc>`, `<rtc>` and `<rb>` elements:
+
+10312002MonthDayYearExpiration Date