Wrapped header motion up with header level changing functions. use
g:vimwiki_header_mode = 0|1 to enable it or not. In header mode, = acts
as the prefix command, following characters are parsed as header
manipulation command.  = for adding level, - for removing level, c for
go to current header, u for going upper header, ] for next, [ for
previous, } for next sibling, } for previous sibling