Syntax highlight and correctly format/manipulate lists

Adds support for syntax highlighting and formatting both ordered and
unordered lists (excluding unordered lists delimited with `*`, as they
conflict with headings and are generally not recommended).

e.g.

    1. Foo
    2. Bar
       1) Biz
       2) Baz

    - Foo
      - Bar
    + Biz
      + Baz

TODO

@@ -1,6 +1,6 @@
 MAYBE:
   - Better link syntax highlighting (more similar to links in vim-markdown)
-  - Syntax highlight bullets and checkboxes
+  - Syntax highlight checkboxes and checkbox cookies
   - Different syntax group for heading delimiters
 
 UNLIKELY:

ftplugin/org.vim

@@ -11,6 +11,9 @@
 "   Web: <https://orgmode.org/manual/index.html>
 
 setlocal commentstring=#%s
+setlocal comments=fb:*,fb:-,fb:+,b:#,b:\:
+setlocal formatoptions+=ncqlt
+let &l:formatlistpat = '^\s*\(\d\+[.)]\|[+-]\)\s\+'
 
 setlocal foldexpr=org#fold_expr()
 setlocal foldmethod=expr

syntax/org.vim

@@ -85,6 +85,13 @@ highlight def link orgTodo Todo
 highlight def link orgTag Type
 
 
+" Lists
+syntax match orgUnorderedListMarker "^\s*[-+]\s\+" keepend contains=@Spell
+syntax match orgOrderedListMarker "^\s*\d\+[.)]\s\+" keepend contains=@Spell
+highlight def link orgUnorderedListMarker Statement
+highlight def link orgOrderedListMarker orgUnorderedListMarker
+
+
 " Timestamps
 syntax match orgTimestampActive /<\d\{4}-\d\{2}-\d\{2}.\{-}>/ keepend
 syntax match orgTimestampInactive /\[\d\{4}-\d\{2}-\d\{2}.\{-}\]/ keepend