Add type signatures to jenksy

[cheginit]

Per the discussion in #118, this PR does the following:

• Add numba type signatures to _fisher_jenks_means
• Remove sort argument from _fisher_jenks_means since it's not being passed from the class function and is always True.
• Add a new extra_req to setup.py for installing numba as speedups.
• Add __pycach__ to .gitignore since numba compiles the function and keep in the cache folder.
• Warn the user if numba is not installed the (slow) pure Python code is used.

[cheginit]

Two of the greedy tests fail and since they are not related to this PR I didn't attempt to address them.

[martinfleis]

(sorry for closing and reopening, I wanted to make sure CI kicks in)

[cheginit]

Sure. No problem! The tests in the CI are passing. However, I used Python 3.10 and latest versions of the dependencies to run pytest on my machine and two of the greedy tests failed. Looking at the source code, the problem seems to be with the latest version of networkx. The assertions fail.

[cheginit]

I used tox-conda with the following config and all tests pass. I am not sure why three of the CI's were stuck for 3 hours.

[tox]
envlist =
    {py36,py37,py38}-{speedup,slow}

[testenv]
conda_deps=
    pytest
    pytest-cov
    codecov
    geopandas
    libpysal
    networkx
    palettable
    speedup: numba
commands=
    pytest {posargs}

[martinfleis]

The PR looks okay to me! Thanks!

However, I used Python 3.10 and latest versions of the dependencies to run pytest on my machine and two of the greedy tests failed.

You can ignore that. I'll make a PR slimming down our CI matrix and including python 3.10 and look into this.

I am not sure why three of the CI's were stuck for 3 hours.

don't know either

[martinfleis]

two of the greedy tests failed.

See networkx/networkx#3993

[cheginit]

Oh. So the issue has been there for a while.

Sounds good! Let me know if this PR needs any other changes.

[cheginit]

It's been a while since I opened this PR, do I need to change anything in this PR?