Nprime

Lighten `nprime` package leaving only the essential.

Update of the sieve of erathostene
Add Trial Division algorithm

Well it's a bit of a stretched and mainly to test the release feature.
Let's get a release.

To read for next time: [http://semver.org/](http://semver.org/)

First version of it on [pypi](https://pypi.org/project/nprime/) due to naming problem, it had to be changed to another name:

> PyPrime is dead long live nprime

It is always sad to change name, but as of now we're online!