* 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
* refactor: moved loading to new module
* refactor: check_single_separator
* refactor: simplified separator fixing
* refactor: tests/ -> lua/tests/
* refactor: moved to nvim_err_writeln for errors
* feat: moved config parsing to config.lua
* feat: get config directly from config module
* feat: added load_all function
* tests: config parsing tests
* added assert to luacheck globals