support a comma-separated list of button names
support a comma-separated list of button names

Previously, only a single button could be disabled via the attribute when 
set in the HTML without the help of JS.  Now, the attribute accepts a
comma-separated list of button names so that more than one button
can be simultaneously hidden.
concats/bootstrap-markdown,fathomlabs/materialize-markdown,acrobat/bootstrap-markdown,toopay/bootstrap-markdown