Foc

- Added `intersperse` and `intercalate`
- Some modifications on functions related to path

- Added symbolic operators (the same notations as the python standard library)
- Fix neatly formatter
- Added a few of basic functions

- Modified folding functions: `foldl`, `foldr`, `foldl1`, `foldr1`, `scanl`, `scanr`, `scanl1`, and `scanr1`
- Added pytest

- First public release