- Added some doc tests
- Minor reformatting

- More documentations are added.
- Also adjusted some formatting.

- Merged imports
- By enabling `clippy::all` and `clippy::pedantic` lints,
 - Marked several methods as `must_use`
 - Found a redundant closue ( `Bins::len` is also more informative on the type
 than `|e| e.len()` )

`left inclusive` and `right exclusive` are not standard math terminology.
It should be phrased as `left-closed` and `right-open`.

`Out of bound` -> `Out of bounds`
`Out-of-bound` -> `Out-of-bounds`

- Rewrites and reformats docs. Hopefully it's more aligned to the style in std
 library.
- Replaced `left-inclusive-right-exclusive` by `left-closed-right-open`, which
 is more common in maths.

- Added `missing_docs` lints from `rustc`
- Added `clippy::all` and `clippy::pedantic` lints
 - Marked methods with `must_use`
 - Improved code style according to clippy

- Added more information in mod-level documentation, including
 - A section for strategies currently implemented
 - A section for requirement of data to infer optimal parameters
- Reformatting

- Added `missing_docs`, `clippy::all`, and `cippy::pedantic` lints
 - They helped to find certain problems when casting values into other types,
 none of the warning is relavant and are suppresed and commented
 - It also warns that the private function `bin_width` doesn't consume the
 input, so their type signature can be changed to a reference. But actually
 this is because this function `clone`ed the inputs. This is not a good
 pattern as it hides the clones. It's better to leave this to the caller and
 make the clone explicit. So this commit removed the `clone` inside of this
 function, and documented that the inputs would be consumed.