Update heading ID computation

Author: rstacruz

HISTORY.md

@@ -4,6 +4,7 @@
 - Markdown code is now stripped out of TOC names
 - The first page will always be the home page
 - You can now link Table of Contents as part of the site
+- Make heading ID's match what GitHub expects
 
 ## [v0.2.0]
 > Oct 12, 2015

lib/slugify.js

@@ -15,5 +15,6 @@ module.exports = function slugify (str) {
   str = str.replace(/\/index.html$/, '')
   str = str.replace(/.html$/, '')
   str = parameterize(str)
+  str = str.replace(/[^a-zA-Z0-9\-_]/g, '')
   if (str.length) return str
 }

test/slugify_test.js

@@ -14,4 +14,11 @@ describe('slugify', function () {
   test('usage.html', 'usage')
   test('/foo/index.html', 'foo')
   test('index.html', 'index')
+  test('page(callback)', 'pagecallback')
+  test('page(path, callback[, callback ...])', 'pagepath-callback-callback-')
+  test('context#save', 'contextsave')
+  test('404 behavior', '404-behavior')
+  test('IE8+', 'ie8')
+  test('Hi (optional):', 'hi-optional')
+  test('a  b  c', 'a-b-c')
 })