Cross prime meridian fix

[ellesmith88]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes issue Fix the "0 degree meridian" issue in subsetting #35
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• HISTORY.rst has been updated (with summary of main changes)
• bumpversion minor has been called on this branch
• I have added my relevant user information to AUTHORS.md

• What kind of change does this PR introduce?:
  Bug fix - where the subset request crosses the meridian but the longitudes are all positive, this implements a method to roll the dataset and reassign the coordinates to allow this subset to take place

• Does this PR introduce a breaking change?:
  I don't think so

• Other information:
  This also removes pyyaml from the requirements - I added this before the 5.4 of pyyaml version was released on conda to allow the docs to build. This version has now been released so this is no longer needed.

[agstephens]

@huard @Zeitsperre This is our fix for coping with bounding box subsets where the requested longitude range does not overlap with the longitudes of the data itself. We believe there are no issues from your end because all the changes are dealt with in clisops.ops.subset and we haven't touched clisops.core.subset.

Please shout if you spot any problems with this. We plan to merge it tomorrow morning (UK time).

[Zeitsperre]

Wow! This is a spotless fix. I'm glad to see that it doesn't roll the data on the core utilities, and it seems to address the concerns you had around this. Nicely done.

Just a thought, but maybe it would be interesting to (in another PR) implement a fix on the core side that turns a bounding box into a shape in the event that it crosses the meridian/edge of the data set and sends that to the subset_shape function? It would be interesting if we could offer both approaches in CLISOPS eventually (rolling and vector-splitting).

[ellesmith88]

@Zeitsperre Thanks for the review. Sounds like a good idea - I've opened an issue for it #119