Fix errors due to numpy deprecation; split required packages further; update specs

[jihaekor]

I had a need to fit CHAID trees, and I had to update a few minor places in the code to get it to work with the latest packages (namely, numpy). This PR makes those updates and also pushes some of the package dependencies to be optional to reduce the size of the installation.

• Fixes errors due to numpy deprecation of np.float and np.int. Updated each to np.float64 and np.int64.
• Added a new split_groups property in the Split class, which just returns the groupings as an actual list rather than the string representation of it.
• Split the required packages into two additional optional groups: graph (needed for generation of graphs, which isn't a core functionality needed to build the trees, per se) and spss (only needed for the initial import)
• Updated the CircleCI specs to the latest images, including newer Python versions (3.9, 3.10, 3.11)

[Rambatino]

Thank you very much for this @jihaekor! 💛

I wonder why the tests aren't running on here - could it be that I must push? It could be some old api keys or something.

Eitherway, will run it later today and merge and release if all good!

[Rambatino]

Looks like it should run...

[jihaekor]

@Rambatino I think that was because I had the CircleCI running on my private forked repository - sorry about that. I unfollowed on my side and pushed up an update to the README (to add some blurbs about the optional package installations) to force the tests to fire.

[codecov[bot]]

Codecov Report

Patch coverage: 96.87% and project coverage change: +0.21% :tada:

Comparison is base (c773a87) 92.90% compared to head (3e6568d) 93.11%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #135 +/- ## ========================================== + Coverage 92.90% 93.11% +0.21% ========================================== Files 8 8 Lines 634 654 +20 ========================================== + Hits 589 609 +20 Misses 45 45 ``` | [Files Changed](https://app.codecov.io/gh/Rambatino/CHAID/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mark+Ramotowski) | Coverage Δ | | |---|---|---| | [CHAID/split.py](https://app.codecov.io/gh/Rambatino/CHAID/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mark+Ramotowski#diff-Q0hBSUQvc3BsaXQucHk=) | `94.73% <85.71%> (+0.73%)` | :arrow_up: | | [CHAID/column.py](https://app.codecov.io/gh/Rambatino/CHAID/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mark+Ramotowski#diff-Q0hBSUQvY29sdW1uLnB5) | `91.22% <100.00%> (ø)` | | | [CHAID/graph.py](https://app.codecov.io/gh/Rambatino/CHAID/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mark+Ramotowski#diff-Q0hBSUQvZ3JhcGgucHk=) | `82.53% <100.00%> (+4.53%)` | :arrow_up: | | [CHAID/tree.py](https://app.codecov.io/gh/Rambatino/CHAID/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Mark+Ramotowski#diff-Q0hBSUQvdHJlZS5weQ==) | `96.80% <100.00%> (ø)` | |

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[Rambatino]

https://pypi.org/project/CHAID/5.3.1/#history