Auto set buffer filetype to markdown if checked as md in Simplenote
Auto set buffer filetype to markdown if checked as md in Simplenote

Read "systemtags" property in note to check if indicated as markdown in
Simplenote. If it is then set buffer filetype to markdown

Fixes #49

sanchon/simplenote.vim,kidpixo/simplenote.vim,yuex/simplenote.vim,sanchon/simplenote.vim,mrtazz/simplenote.vim,mrtazz/simplenote.vim