Missing "otherwise" in `hash_append` reference docs

[Lastique]

In this section, each item in Effects seems to be an alternative rather than a step in the sequence. I think, in such cases each item should end with "; otherwise". Or better yet, the Effects should start with a preamble like "Performs one of the following actions".

[pdimov]

"Otherwise" implies that they are tried in order, and the first match wins, which isn't currently the case (for the same reason I haven't made tag_invoke "win" over the rest.)

I've found that ambiguities are generally better reported, than arbitrarily settled.