Add org_clean_folds option

autoload/org.vim

@@ -4,9 +4,23 @@
 " License:      Vim (see `:help license`)
 " Location:     autoload/org.vim
 " Website:      https://github.com/axvr/org.vim
-" Last Change:  2019-09-22
+" Last Change:  2020-01-04
 
 " Fallback chain for options. Buffer local --> Global --> default.
-function org#option(name, default)
+function org#option(name, default) abort
     return get(b:, a:name, get(g:, a:name, a:default))
 endfunction
+
+" Emacs-like fold text.
+function org#fold_text() abort
+    return getline(v:foldstart) . '...'
+endfunction
+
+" Check fold depth of a line.
+function org#fold_expr()
+    let l:depth = match(getline(v:lnum), '\(^\*\+\)\@<=\( .*$\)\@=')
+    if l:depth > 0 && synIDattr(synID(v:lnum, 1, 1), 'name') =~# '\m^o\(rg\|utline\)Heading'
+        return ">" . l:depth
+    endif
+    return "="
+endfunction