adjusting markdoc for Stata 16

• improving the mini engine
• fixing a bug on Windows machines
• improving the linesize for mini engine

• fixing a bug in mdconvert.ado

• fixing a bug in sthlp Markdown tables for Stata help files

• fixing a bug in mdconvert.ado
• adding presentation slides for mini mode, with syntax highlighter
• improving the Stata Help File template
• allowing conversion of markdown tables in Stata Help files
• producing warning if the source file is not in the current working directory

MarkDoc Mini Released!