Spool map

[d-chambers]

Description

This PR:

• Implements a spool.map function for applying a callable to all patches in a spool
• Implements a spool.split function for splitting a spool into sub-spools.
• Improves the docstring of several spool methods.

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes.
• documented the new feature with docstrings or appropriate doc page.
• included a test. See testing guidelines.
• your name has been added to the contributors page (docs/contributors.md).
• added the "ready_for_review" tag once the PR is ready to be reviewed.

[codecov]

Codecov Report

Merging #227 (5ed7053) into master (5a438aa) will increase coverage by 0.01%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #227      +/-   ##
==========================================
+ Coverage   98.85%   98.86%   +0.01%     
==========================================
  Files          75       75              
  Lines        6003     6060      +57     
==========================================
+ Hits         5934     5991      +57     
  Misses         69       69              

Flag	Coverage Δ
unittests	98.86% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
dascore/clients/dirspool.py	100.00% <100.00%> (ø)
dascore/clients/filespool.py	100.00% <100.00%> (ø)
dascore/constants.py	100.00% <100.00%> (ø)
dascore/core/spool.py	100.00% <100.00%> (ø)
dascore/io/prodml/utils.py	100.00% <100.00%> (ø)
dascore/proc/basic.py	100.00% <100.00%> (ø)
dascore/utils/chunk.py	100.00% <100.00%> (ø)
dascore/utils/misc.py	99.27% <100.00%> (+0.05%)	⬆️