* Add DeepSource config
* Simplify if statement
* Refactor use of dict() with empty literal
* Use set comprehension syntax
* Refactor chained comparison
* Rewrite instances of list literal within set() as set literals
* Add test_slow to class definition
* Allow both both hoidays and append holidays
Match holidays in predict and fit
Add test for append_holiday features; minor fixes
Add column name validation for append_holidays names; allow only one country
Fix bug about holiday year different from input year and also other bugs
Change function description
Add append holiday feature for R
* Add test for R/Pyrhon; fix bugs