API cleanup

[d-chambers]

Description

This PR cleans up a few API issues we discussed yesterday in the sprint:

• uses update_coords rather than update_attrs to change attributes in the tutorial
• removes iselect-like methods in favor of a samples argument. This is consistent with rolling, etc.
• deprecates the tran namespace, now transformations are just patch methods
• fixes some internal coordinate APIs (eg drop_coords now accepts positional arguments)

Once #248 is implemented the changes we discussed will be complete.

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.

[d-chambers]

Oops, looks like this branch was based on the wrong branch. it should be fine if we squash and merge though.

[codecov]

Codecov Report

Merging #249 (0d0a4c0) into master (6d5c4d6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #249   +/-   ##
=======================================
  Coverage   99.06%   99.07%           
=======================================
  Files          79       79           
  Lines        6444     6462   +18     
=======================================
+ Hits         6384     6402   +18     
  Misses         60       60           

Flag	Coverage Δ
unittests	99.07% <100.00%> (+<0.01%)	⬆️

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

Files Changed	Coverage Δ
dascore/constants.py	100.00% <ø> (ø)
dascore/transform/__init__.py	100.00% <ø> (ø)
dascore/transform/differentiate.py	100.00% <ø> (ø)
dascore/transform/spectro.py	100.00% <ø> (ø)
dascore/core/attrs.py	100.00% <100.00%> (ø)
dascore/core/coordmanager.py	100.00% <100.00%> (ø)
dascore/core/patch.py	100.00% <100.00%> (ø)
dascore/io/core.py	100.00% <100.00%> (ø)
dascore/proc/__init__.py	100.00% <100.00%> (ø)
dascore/proc/coords.py	100.00% <100.00%> (ø)
... and 7 more

[ahmadtourei]

@d-chambers Would it be ok to include this and #246 in the 0.0.14 release? I have thoroughly tested the current master branch with different data types and operations, and it's ready for release.