Easier installation and fixed a few methods

[fairliereese]

Hi there,
I'm really excited about using hopper. I wanted to make it pip installable to make it easier to run, and I also corrected some of the code to work with test.py and test.ipynb that I could figure out along the way.

Changes:

• After pip installation, methods from hopper (hoppers.py, explore.py, and utils.py) can be run from anywhere using import hopper. Non-class methods must therefore be called as hopper.hopper(data) or hopper.compress(...)
• Updated README.md, test.py, and the part of test.ipynb that I was able to get to work with the new import schema and associated calls
• Fixed calls to compress in test files
• Added "leiden" option to explore.py viz function

Hopefully you find this useful!

[fairliereese]

I want to mention that the last cell that I managed to run in test.ipynb was `

hopper.viz(smallgauss, rep='X', color='leiden', louvain=False, leiden=True)

and that was only after modifying the viz function.

[maxwellkonnaris]

Hey do you mind helping me out with this? It seems like you ran into all the same issues I just did, but this was never merged to main branch and I am not able to use it. I was about to begin writing my own version of this package, but id rather not waste so much time.

[fairliereese]

Oh boy, it's been a while. I would say see if you can just manage to use my branch?