Rstnpy

Improvements

- Removes uses of the os module
- Enhanced the use of the pathlib module

GetRSTN now called RSTNPy for its first official release.

Improvements

- GetRSTN class has been renamed to RSTN.
- Add two new classes to modularize the code.
- RSTNDownloader used to download the rstn files.
- RSTNFile a class used a rstn filename manipulation toolkit.
- Drop support for Python 2.7, now officially supports Python 3.5+
- No need to redownload the file if it already exists.
- Now using only Pathlib instead of the os module.

Replaces wget

Uses requests instead

Fix san vito related errors

- Fix the problems reading san vito files
- Now cast the column values to int64 instead of int16

Update the API to be more concise and user friendly.

- Enhanced the file reading. Now it'll read all the columns, even if
there's data missing. The number are numpy int16, and the missing data
is numpy NaN.
- Refactored lots of methods of the code. Renamed some methods, and
wrote new ones.

This update is all about code refactoring as the lib was kind of a trap
before this update.