feat(subParser/tables.js): add support for md span elements in table headers

+ tests

Closes #179

src/subParsers/tables.js

@@ -15,6 +15,7 @@ showdown.subParser('tables', function (text, options, globals) {
       if (options.tableHeaderId) {
         id = ' id="' + header.replace(/ /g, '_').toLowerCase() + '"';
       }
+      header = showdown.subParser('spanGamut')(header, options, globals);
       if (!style || style.trim() === '') {
         style = '';
       } else {

test/features/tables/#179.parse_md_in_table_ths.html

@@ -0,0 +1,16 @@
+<table>
+  <thead>
+    <tr>
+      <th><em>foo</em></th>
+      <th><strong>bar</strong></th>
+      <th><del>baz</del></th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>100</td>
+      <td>blabla</td>
+      <td>aaa</td>
+    </tr>
+  </tbody>
+</table>

test/features/tables/#179.parse_md_in_table_ths.md

@@ -0,0 +1,3 @@
+| *foo* | **bar** | ~~baz~~ |
+|-------|---------|---------|
+| 100   | blabla  |  aaa    |

test/node/testsuite.features.js

@@ -36,6 +36,8 @@ describe('makeHtml() features testsuite', function () {
     for (var i = 0; i < tableSuite.length; ++i) {
       if (tableSuite[i].name === 'basic_with_header_ids') {
         converter = new showdown.Converter({tables: true, tableHeaderId: true});
+      } else if (tableSuite[i].name === '#179.parse_md_in_table_ths') {
+        converter = new showdown.Converter({tables: true, strikethrough: true});
       } else {
         converter = new showdown.Converter({tables: true});
       }