add g:instant_markdown_update_on_bufwritepost (default is enabled)
at first POST, run curl as foreground and check if POST succeeded
fix indent
add <buffer> <C-l> mapping to update httpd.js page
remove :silent from 'call s:update_markdown()'
add g:instant_markdown_no_default_keymappings
support 'User instant-markdown-mapping' event

allow user to customize mappings after :InstantMarkdownStart was done
add doc/instant-markdown.txt