Improve compile_header function

[kelle]

• [x] Use Messages to provide feedback when header keywords aren't provided.
• [x] Figure out a way to make sure every key in dictionary is added to the header.

[kelle]

If we make the expected keywords a list, we could compare to the dictionary keys as described here: https://stackoverflow.com/questions/15385308/how-to-compare-list-values-with-dictionary-keys-and-make-a-new-dictionary-of-it

[kelle]

For now, if there is a key added that we don't expect, compile_header should fail and instruct the user how to add a new keyword after the header is compiled.

[kelle]

Completed via #365 .