updated ellipsis chars

As discussed in #8593, here are changes to documentation to use midline ellipsis ⋯ to refer to etc., to distinguish from the splice notation ... (three periods in a row). It was confusing because the same string of characters had two different meanings, which could only be distinguished by guessing the author's intent. I believe that ⋯ was intended in the majority of cases, and I have attempted to preserve explicit correct use of splice (...) where appropriate. 

I am new to Julia. I would appreciate if someone could look through all of the many changes to verify their correctness.
I thought about that for a while, and I'm still not sure, but my reasoning is this:

1. First thing worth learning is probably something like Array(Float64, 1) or Array(Float64, 1, 2)
2. Array also accepts a tuple like Array(Float64, (1, 2)) as the text above says
3. There's no need to splat a tuple like Array(Float64, (1,2)...) which is the same as syntax 2
4. You _can_ splat an array like Array(Float64, [1, 2]...) which doesn't work without the ... but I would consider this to be a less-used case. And if you understand syntax 1 and you (separately) learn about splatting/splicing, then this one is automatic

Of course, I can't get into the mind of the original author. The most difficult cases for me were ones like this, which perhaps should be written with a comma such as Array(type, dim, ⋯) to reduce ambiguity. But the fact that it's ambiguous is all the more reason why it should be clarified one way or another.