Make plugin reloadable
Make plugin reloadable

there was a call to s:init() missing in the toggle function.
Without it, it wouldn't reload correctly, since the s:initialized
variable would never be set to 1 again. So load it when setting up
everything correctly.

fixes #1842

yzhou61/vim-airline,chrisbra/vim-airline,rchicoli/vim-airline,bling/vim-airline