The changelog textbox supports all the same formatting as the description textbox; it just doesn't have a formatting toolbar. If you don't know all the BBCode tags, or don't want to type them, you can just prepare your changelog in a comment/forum posting forum and then copy and paste it into the textbox.
I glanced at your changelog for your most recently updated addon (SliceCommander) and I'd actually suggest using a[list] instead of[indent] tags to format your lists of additions and changes:
All the things
__________________ Retired author of too many addons.
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