Spelling consistency

[mcdittmar]

The document could use a sweep for consistency of British vs American spelling.
Noticed with respect to the word "analyse" vs "analyze"

I'm submitting an issue rather than making a PR because I'm not sure which way is preferred.

[mservillat]

I went through the text and opted for the terms that were more often used in the Note, i.e. mostly British. Going through other IVOA documents, there is no clear consistency ! but we should at least find some consistency in this Note.

I also searched for trends, but there is no clear best choice !
https://trends.google.com/trends/explore?q=analyse,analize
https://trends.google.com/trends/explore?q=visualize,visualise
--> analySe and visualiZe are the spellings found more often...