doc/rst2html: some few fixes for enumerated and bullet lists (#16295)

* fix bullet/enumarated lists with many blank lines
* fix enumerated list parsing
* fix parse failure when next line after list empty
* implement arbitrary start of enumerator
* check that enumerators are in order
* remove redundant start=x if x=1 or a
* add some doc on implemented features
* update start in rst_examples.rst
* allow upper-case letters + more docs

config/nimdoc.tex.cfg

@@ -50,6 +50,7 @@ doc.file = """
 \usepackage{fancyvrb, courier}
 \usepackage{tabularx}
 \usepackage{hyperref}
+\usepackage{enumitem}
 
 \begin{document}
 \title{$title $version}