Syracuse

Add a new module: `sequences`
This module provides several well-known sequences related to Collatz sequences.
For the moment, the available sequences are:

| sequence | [OEIS](https://oeis.org/) reference | Description |
| -------- | ----------------------------------- | ----------- |
| total_stopping_time_records | A006877 | Sequence of starting values of Collatz sequences with a total stopping time longer than of any smaller starting value. |
| max_value_records | A006884 | Sequence of starting values of Collatz sequences with maximum values higher than of any smaller starting value. |

- Add usage of multitasking for some computations on large data
- Introduction of an optional usage of the `pydot` library to generate `dot` files
- Add the ability of generating a distribution bar graph for a range of sequences

Adds the ability to switch to multiprocessing computation for several Syracuse class methods, improving drastically performance for large amount of data.

Fix an issue making the image on `README.md` not displayable on Pypi

Add some information for publishing on Pypi

First release