Replace calls to append with setline()

- Using append created an extraneous line when opening a zoom buffer which would
  then be written back to the original file.  Setline simply overwrites the
  lines that are present when the buffer is open so there is no extraneous line
  when using it.
Change default to zoom out on write
Default g:mazda_default_mappings to 1
Add headers to delimit sections
Change version to 0.3 in mazda.vim