Feature: Markdown: Support SetExt Heading (Issue #209)

Like these
==========

See: https://spec.commonmark.org/0.29/#setext-headings

Note: work for follow_link and VimwikiTOC

syntax/vimwiki.vim

@@ -186,6 +186,18 @@ for s:i in range(1,6)
         \ '/me=s-1 transparent fold'
 endfor
 
+" SetExt header
+" TODO mutualise SetExt Regexp
+let setex_header1_re = '^\s\{0,3}[^>].*\n\s\{0,3}==\+$'
+let setex_header2_re = '^\s\{0,3}[^>].*\n\s\{0,3}--\+$'
+execute 'syntax match VimwikiHeader1'
+    \ . ' /'. setex_header1_re . '/ '
+    \ 'contains=VimwikiTodo,VimwikiHeaderChar,VimwikiNoExistsLink,VimwikiCode,'.
+    \ 'VimwikiLink,@Spell'
+execute 'syntax match VimwikiHeader2'
+    \ . ' /'. setex_header2_re . '/ ' .
+    \ 'contains=VimwikiTodo,VimwikiHeaderChar,VimwikiNoExistsLink,VimwikiCode,'.
+    \ 'VimwikiLink,@Spell'
 
 
 let s:options = ' contained transparent contains=NONE'

syntax/vimwiki_markdown.vim

@@ -63,8 +63,25 @@ let s:markdown_syntax.rxMultilineCommentEnd = ''
 let s:markdown_syntax.rxComment = '^\s*%%.*$\|<!--[^>]*-->'
 let s:markdown_syntax.rxTags = '\%(^\|\s\)\@<=:\%([^:[:space:]]\+:\)\+\%(\s\|$\)\@='
 
-let s:markdown_syntax.header_search = '^\s*\(#\{1,6}\)\([^#].*\)$'
-let s:markdown_syntax.header_match = '^\s*\(#\{1,6}\)#\@!\s*__Header__\s*$'
+
+" Used in code (base.vim)
+"""""""""""""""""""""""""
+
+" Header
+" TODO mutualise with rxHeader in vars.vim := Define atx_regex only onces
+" TODO regex_or function  => (1|2)
+let atx_header_search = '^\s*\(#\{1,6}\)\([^#].*\)$'
+let atx_header_match  = '^\s*\(#\{1,6}\)#\@!\s*__Header__\s*$'
+
+let setex_header_search = '^\s\{0,3}\zs[^>].*\ze\n'
+let setex_header_search .= '^\s\{0,3}[=-]\{2,}$'
+
+let setex_header_match = '^\s\{0,3}>\@!__Header__\n'
+let setex_header_match .= '^\s\{0,3}[=-][=-]\+$'
+
+let s:markdown_syntax.header_search = '\%(' . atx_header_search . '\|' . setex_header_search . '\)'
+let s:markdown_syntax.header_match = '\%(' . atx_header_match . '\|' . setex_header_match . '\)'
+
 let s:markdown_syntax.bold_search = '\%(^\|\s\|[[:punct:]]\)\@<=\*\zs'.
       \ '\%([^*`[:space:]][^*`]*[^*`[:space:]]\|[^*`[:space:]]\)\ze\*\%([[:punct:]]\|\s\|$\)\@='
 let s:markdown_syntax.bold_match = '\%(^\|\s\|[[:punct:]]\)\@<=\*__Text__\*'.