Feat imaging maps

[samaloney]

• Update demo to use images and create sunpy maps using the header helper.
• Fix ELUT lookup to use the corresponding science energy channels
• Small doc and docstring updates

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.92%. Comparing base (a35a42c) to head (6e8ddc7).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #107      +/-   ##
==========================================
+ Coverage   68.47%   68.92%   +0.44%     
==========================================
  Files          31       31              
  Lines        1843     1847       +4     
==========================================
+ Hits         1262     1273      +11     
+ Misses        581      574       -7     

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