Update HTML files.

* Move meta charset first
* Remove unneeded default script type
* fix some validation errors from index.html
Trim trailing spaces and convert tabs to spaces.
index.html: use the relative link to 2.x pages.
Revert the validation fixes until the problem is reported and fixed upstream in gh-buttons.
2.x pages: use html5shiv from OSSCDN like the Bootstrap docs.
Merge pull request #210 from XhmikosR/gh-pages

Tweak HTML files