Offsets, xclass for span

Added offsets and xclass to span tags
Lead tag and do_shortcode for collapsibles.
Merge branch 'bootstrap3' of https://github.com/simonyeldon/bootstrap-shortcodes into bootstrap3

Conflicts:
	README.md
	bootstrap-shortcodes.php
Merge branch 'bootstrap3' of https://github.com/simonyeldon/bootstrap-shortcodes

Conflicts:
	README.md
	bootstrap-shortcodes.php
Fix accordions/panels, add list groups
Add List Groups to documentation
Remove extra P's from panels added by WordPress
Default collapse to closed.
Merge pull request #1 from FoolsRun/bootstrap3

Merge #1 in to Bootstrap3. 

Thanks for the help