Remove initialize method from archives

[eszabo12]

Description

I put the solution_dim (int): Dimension of the solution space. As the comment under args above the stuff. I put the solution_dim argument s.t. The new prototype for init in _archive_base is def init(self, cells, behavior_dim, solution_dim, seed=None, dtype=np.float64) for archive_base.
The new prototype for cvt_archive is def init(self,
cells,
ranges,
solution_dim,
seed=None,
dtype=np.float64,
samples=100_000,
custom_centroids=None,
k_means_kwargs=None,
use_kd_tree=False,
ckdtree_kwargs=None)
The new prototype for grid_archive is def init(self, dims, ranges, solution_dim, seed=None, dtype=np.float64)

I put solution_dim as a required (non-default) arg before seed in every instance.

TODO

• Remove the archive.initialize() calls from the tests, because they are now deprecated and shouldn't work.
• Comment line 61 in ribs/optimizers/_optimizer.py that calls the initialize function
• Fix the comment in __init__.py that says ".. note:: After construction, each archive must be initialized by calling
  its initialize() method before it can be used"
• Remove decorator from the install_requires in setup.py since it was only used for require_init

Questions

• Are there any issues/unideal things about my changes to the documentation/commenting, etc
• The output of pytest had a lot of issues, should I go through them systematically? i.e., there is an unused import on line 7 of _cvt_archive.py-- the require_init function.

Status

• I have read the guidelines in CONTRIBUTING.md.
• I have formatted my code using yapf
• I have tested my code by running pytest
• I have linted my code with pylint
• I have added a one-line description of my change to the changelog in HISTORY.md.
• This PR is ready to go

[btjanaka]

Make sure to remove the call to initialize in the Optimizer, and remove/fix any tests. Also, try running the example code from the pyribs home page to make sure everything still works.

[btjanaka]

Minor changes

[btjanaka]

minor