For now use a dummy component to lualine_x on extensions that only define
lualine_a. This will let the renderer know right sections do exist.
closes#73
* Deprecate upper & lower option.
These does not make much sense and `format` option can provide same results
* Unify padding options
* Add persistent notices
* Make separators use left/right keys to specify left right instead of
sequence
* Rename format -> fmt
* Rename condition -> cond
* Rename disable_text -> icon_only
* Unify color_error,warning,info,hint under diagnostics_color
* Unify color_added,modified,removed hint under diff_color