Add support for label positioning

[jsolbrig]

Requested Update

Description

We would like to add support for lat/lon label positioning. This should be controllable via gridlines plugins.

Background and Motivation

See this comment: #140 (comment)

Checklist for Completion

• Update gridlines schema to support label positioning
• Update code to support label positioning
• Develop tests to ensure that this produces repeatable repositioning of labels
• Update documentation to describe how to control label positions

[evrose54]

@jsolbrig is there an example image you could add to this issue that demonstrates how Tim Olander wants to position his labels? I think that would help me moving forward on this issue.

[jsolbrig]

@evrose54 This would be a matter of exposing more options from the GridlineAnnotator to allow changing position, size, and format of lat/long labels. For example, we might move the labels inside the axes instead of outsize.

Ask Jeremy for some actual image examples if you have questions.