v0.8-beta: Release 0.8-β

This release has been mostly code refactoring, with few minor extras such as
making persimmon pipeable.

Code
* Persimmon is now registered at Pypi.
* Refactored some loops in favor of generator expression/list comprehensions.
* Annotated part of the codebase with type hinting.
* Refactored property in derived class.
* Implemented abstract classes that enforce overriding.

Documentation
* Updated README.
* Fixed LaTeX cover template.

The LaTeX documentation will probably move to its own repository soon.