Added
* This changelog!
* Python 3.6 as package dependency.
* `__version__` in `__init__.py`.
* `TODO.md`
* Transformation functions that tricker class methods (`rvpy.log()`, `rvpy.exp()`, `rvpy.pow()`, etc.)
* **Logistic distribution**.
* **Log-Logistic distribution**.
* **Gumbel distribution**.
* **Gompertz distribution**.
* **Degenerate distribution**.