category.xml: fixed broken link
buttons.xml: moved the code examples to be html rather than xhtml
checkboxradio.xml: moved the code examples to be html rather than xhtml
collapsible.xml: added missing spaces after ':'
categories.xml: use warning div rather than inline style
checkboxradio.xml: added the warning div where necessary, in-line with core and ui
Flipswitch: Document CSS changes necessary for achieving correct indentation for custom labels, and correct widget sizing for even longer custom labels.

Re: https://github.com/jquery/jquery-mobile/issues/6729
Flipswitch: Document options "onText" and "offText".