backporting syntax file from vim-pandoc/vim-pandoc-syntax
update pandoc syntax from vim-pandoc-syntax
fail gracefully if yaml syntax file isn't found
update pandoc syntax from vim-pandoc-syntax
Update from vim-pandoc-syntax
updated syntax file from vim-pandoc-syntax
fix citations with accented characters
Merge branch 'backport-pandoc-syntax'

This will make sure many of the syntax issues get fixed for a lot of users.
However, a notice will be made soon that syntax changes happen on vim-pandoc-syntax repo first, and are only later (if ever) backported here.
added a note to the documentation on vim-pandoc's new organization.