convert VimWiki to markdown using Vim


* Convert bold: %s/\*\(.*\)\*/**\1**/g
* Convert named link: %s/\[\[\(.\{-}\)|\(.\{-}\)\]\]/[\2](\1)/g
* Convert link: %s/\[\[\(.\{-}\)\]\]/<\1>/g
* Title: 
  * First: %s/= \(.*\) =/# \1/g
  * May multiple: %s/=\(.*\)=/#\1/g
* Picture: %s/{{\(.\{-}\)}}/![](\1)/g
* Fenced code start: %s/{{{class="brush:\(.*\)"/```\1/g
* Fenced code end: %s/}}}/```/g
* Manual change # ordered list