This adds support for alphabetical lists in org by enabling the
extension Ext_fancy_lists, mimicking the behaviour of Org Mode when
org-list-allow-alphabetical is enabled.
Enabling Ext_fancy_lists will also make Pandoc differentiate between the
delimiters of ordered lists (periods or closing parentheses). Org does
this differentiation by default when exporting to some formats (e.g.
plain text) but does not in others (e.g. html and latex), so I decided
to copy Pandoc's markdown reader behaviour.
