Refactor prune_local

[ahill187]

Description

In this PR:

1. Renamed make_csrmatrix_noselfloop -> prune_local
2. Renamed keep_all_local_dist -> do_prune_local, with the opposite meaning, i.e. do_prune_local = True is the same as keep_all_local_dist = False
3. Added docstrings
4. Added l2_std_factor as argument
5. Removed unused discard_count
6. Added tests for prune_local
7. Renamed the following variables:

original	new
distlist	distances
row	neighbors
updated_nn_ind	updated_neighbors
updated_nn_weights	updated_distances
ik	index
rowi	community_id
csr_graph	csr_array
dist	distance
keep_all_local_dist	do_prune_local (opposite)

See ShobiStassen#37.

Note
There was a previous PR: #5, which was similar to this one. The reason I am re-doing the PR is because the first refactor, PR #2, was too large, so I am splitting up that PR and subsequent PRs and merging them into master instead of main. Then I can create smaller PRs to merge into the original repo at https://github.com/ShobiStassen/PARC.