remove table headers that are completely empty

NEWS.md

@@ -1,5 +1,7 @@
 # CHANGES IN litedown VERSION 0.5
 
+- Empty table headers are removed in HTML output (they may be generated from data frames or matrices without column names).
+
 - `pkg_manual()` will point out the name of the problematic Rd file when the Rd file fails to convert to HTML (thanks, @BSchamberger).
 
 - Dropped **knitr** and **rmarkdown** from the `Suggests` field in `DESCRIPTION`. Previously, **litedown** allowed `rmarkdown::render()` to use the output formats `litedown::html_format` and `litedown::latex_format`. Now `rmarkdown::render()` is no longer supported, and `litedown::fuse()` must be used instead.

R/mark.R

@@ -272,6 +272,8 @@ mark = function(input, output = NULL, text = NULL, options = NULL, meta = list()
     }, 'html', function(z2) gsub(id4, ' ', restore_html(z2)))
     # some code blocks with "attributes" are verbatim ones
     ret = match_replace(ret, '```+\\{.+}', function(x) gsub(id4, ' ', x, fixed = TRUE))
+    # remove empty table header
+    ret = gsub('<thead>\n<tr>\n(<th[^>]*></th>\n)+</tr>\n</thead>\n', '', ret)
     # table caption: a paragraph that starts with 'Table: ' or ': ' after </table>
     ret = gsub(
       '(<table>)(?s)(.+?</table>)\n<p>(Table)?: (?s)(.+?)</p>',