Change logic for converting GET-params to a filename

[JaZo]

Description

I replaced Stringy->slugify with a less destructive method and we don't replace = and & characters.

Motivation and context

The current logic for converting the GET-params to a filename is too strict and can lead to collisions. This fixes #1 by making the logic looser and collisions less likely as discussed.

Please note that this is a breaking change!

How has this been tested?

Tested using updated and existing tests.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply.

• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.